Showing papers by "Chalk River Laboratories published in 2012"
TL;DR: The temperature dependence of bilayer parameters obtained using the one-dimensional scattering density profile model - which was derived from molecular dynamics simulations - including the area per lipid, the overall bilayer thickness, as well as other intrabilayer parameters (e.g., hydrocarbon thickness).
198 citations
TL;DR: In this article, the influence of uniaxial magnetocrystalline anisotropy on the magnetic textures that are formed in a chiral magnetic system was investigated, and it was shown that the epitaxially induced tensile stress in MnSi thin films grown on Si(111) creates an easy-plane anisotropic effect.
Abstract: We present an experimental and theoretical investigation of the influence of a uniaxial magnetocrystalline anisotropy on the magnetic textures that are formed in a chiral magnetic system. We show that the epitaxially induced tensile stress in MnSi thin films grown on Si(111) creates an easy-plane uniaxial anisotropy. The magnetoelastic shear stress coefficient is derived from SQUID magnetometry measurements in combination with transmission electron microscopy and x-ray diffraction data. Density functional calculations of the magnetoelastic coefficient support the conclusion that the uniaxial anisotropy originates from the magnetoelastic coupling. Theoretical calculations based on a Dzyaloshinskii model that includes an easy-plane anisotropy predict a variety of modulations to the magnetic order that are not observed in bulk MnSi crystals. Evidence for these states is found in the magnetic hysteresis and polarized neutron reflectometry measurements.
100 citations
TL;DR: In this article, the authors combine molecular dynamics simulations and experiment, both small-angle neutron (SANS) and smallangle X-ray scattering (SAXS), to determine the precise structure of bilayers composed of 1-palmitoyl-2-oleoyl -sn-glycero-3-phosphatidylglycerol (POPG), a lipid commonly encountered in bacterial membranes.
Abstract: We combine molecular dynamics (MD) simulations and experiment, both small-angle neutron (SANS) and small-angle X-ray scattering (SAXS), to determine the precise structure of bilayers composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG), a lipid commonly encountered in bacterial membranes. Experiment and simulation are used to develop a one-dimensional scattering density profile (SDP) model suitable for the analysis of experimental data. The joint refinement of such data (i.e., SANS and SAXS) results in the area per lipid that is then used in the fixed-area simulations. In the final step, the direct comparison of simulated-to-experimental data gives rise to the detailed structure of POPG bilayers. From these studies we conclude that POPG s molecular area is 66.0 +/- 1.3 ^2, its overall bilayer thickness is 36.7 +/- 0.7 , and its hydrocarbon region thickness is 27.9 ( 0.6 , assuming a simulated value of 1203 ^3 for the total lipid volume.
91 citations
TL;DR: Molecular dynamics simulations and experiment are used to develop a one-dimensional scattering density profile (SDP) model suitable for the analysis of experimental data and the direct comparison of simulated-to-experimental data gives rise to the detailed structure of POPG bilayers.
73 citations
TL;DR: In this article, the antiferromagnetic (AF) phase appears to overlap with the superconducting phase in some materials such as BaFe2-xTxAs2 (where T = Co or Ni).
Abstract: Superconductivity in the iron pnictides develops near antiferromagnetism, and the antiferromagnetic (AF) phase appears to overlap with the superconducting phase in some materials such as BaFe2-xTxAs2 (where T = Co or Ni). Here we use neutron scattering to demonstrate that genuine long-range AF order and superconductivity do not coexist in BaFe2-xNixAs2 near optimal superconductivity. In addition, we find a first-order-like AF-to-superconductivity phase transition with no evidence for a magnetic quantum critical point. Instead, the data reveal that incommensurate short-range AF order coexists and competes with superconductivity, where the AF spin correlation length is comparable to the superconducting coherence length.
68 citations
TL;DR: It is demonstrated in BaFe2As2 samples detwinned via uniaxial strain that the in-plane C4 symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures.
Abstract: We report neutron scattering experiments probing the influence of uniaxial strain on both the magnetic and structural order parameters in the parent iron pnictide compound, ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$. Our data show that modest strain fields along the in-plane orthorhombic $b$ axis can affect significant changes in phase behavior simultaneous to the removal of structural twinning effects. As a result, we demonstrate in ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ samples detwinned via uniaxial strain that the in-plane ${C}_{4}$ symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures. Surprising changes in the magnetic order parameter of this system under relatively small strain fields also suggest the inherent presence of magnetic domains fluctuating above the strain-free ordering temperature in this material.
67 citations
TL;DR: Direct experimental evidence is presented that ASA molecules participate in saturated lipid bilayers of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) and preferably reside in the head group region of the membrane.
Abstract: We studied the interaction of Aspirin (acetylsalicylic acid) with lipid membranes using x-ray diffraction for bilayers containing up to 50 mol% of aspirin. From 2D x-ray intensity maps that cover large areas of reciprocal space we determined the position of the ASA molecules in the phospholipid bilayers and the molecular arrangement of the molecules in the plane of the membranes. We present direct experimental evidence that ASA molecules participate in saturated lipid bilayers of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) and preferably reside in the head group region of the membrane. Up to 50 mol% ASA molecules can be dissolved in this type of bilayer before the lateral membrane organization is disturbed and the membranes are found to form an ordered, 2D crystal-like structure. Furthermore, ASA and cholesterol were found to co-exist in saturated lipid bilayers, with the ASA molecules residing in the head group region and the cholesterol molecules participating in the hydrophobic membrane core.
59 citations
TL;DR: A detailed study of magnetism in LuFe(2)O(4), combining magnetization measurements with neutron and soft x-ray diffraction, finding that for both phases the spin structure is refined by neutron diffraction.
Abstract: We present a detailed study of magnetism in LuFe(2)O(4), combining magnetization measurements with neutron and soft x-ray diffraction. The magnetic phase diagram in the vicinity of T(N) involves a metamagnetic transition separating an antiferro- and a ferrimagnetic phase. For both phases the spin structure is refined by neutron diffraction. Observed diffuse magnetic scattering far above T(N) is explained in terms of near degeneracy of the magnetic phases.
54 citations
TL;DR: In this paper, a combined neutron and X-ray scattering investigation was conducted to study the effect of ethanol on the molecular structure and dynamics of lipid membranes, finding that the ethanol molecules reside in the head group region of the bilayers, with 1.6 ethanol molecules per lipid molecule in the gel phase and 1.2 ethanol molecules in the fluid phase.
Abstract: We present a combined neutron and X-ray scattering investigation to study the effect of ethanol on the molecular structure and dynamics of lipid membranes. 1,2-Dimyristoyl-sn-glycero-3-phoshatidylcholine (DMPC) powder hydrated with a 5 wt% ethanol solution (corresponding to 2 mol% of ethanol) was used in this study. From high-resolution X-ray experiments the position and partitioning of the ethanol molecules in the phospholipid bilayers was determined in their gel and fluid phases. We find that the ethanol molecules reside in the head group region of the bilayers, with 1.6 ethanol molecules per lipid molecule in the gel phase and 1.2 ethanol molecules per lipid molecule in the fluid phase. We find evidence for enhanced permeability in both fluid and gel phases of the phospholipid bilayers in the presence of ethanol molecules. Elastic and quasi-elastic neutron scattering data, obtained using a neutron backscattering spectrometer, was used to study slow, nanosecond molecular dynamics on length scales corresponding to lipid diffusion, acyl chain dynamics and solvent dynamics. While the presence of ethanol molecules had no observable effect on these types of dynamics in the fluid (Lα) phase, the membranes appeared to have a higher degree of order in gel (Lβ) and ripple (Pβ′) phases. In particular, lipid diffusion was found to be slower by a factor of two in the more rigid gel phase when ethanol was present.
53 citations
TL;DR: In this article, the authors present direct experimental evidence for the co-existence of gel and fluid lipid domains in a single-component phospholipid membrane made of DPPC as it undergoes its main phase transition.
Abstract: Lateral nanostructures in membranes, so-called rafts, are believed to strongly influence membrane properties and functions. The experimental observation of rafts has proven difficult as they are thought to be dynamic structures that likely fluctuate on nano- to microsecond time scales. Using neutron diffraction we present direct experimental evidence for the co-existence of gel and fluid lipid domains in a single-component phospholipid membrane made of DPPC as it undergoes its main phase transition. The coherence length of the neutron beam sets a lower limit for the size of structures that can be observed. Neutron coherence lengths between 30 and 242 A used in this study were obtained by varying the incident neutron energy and the resolution of the neutron spectrometer. We observe Bragg peaks corresponding to co-existing nanometer sized structures, both in out-of-plane and in-plane scans, by tuning the neutron coherence length. During the main phase transition, instead of a continuous transition that shows a pseudo-critical behavior, we observe the co-existence of gel and fluid domains.
43 citations
TL;DR: In this paper, the correlated ground state in the bilayer iridium oxide was explored through a neutron scattering, charge transport, and magnetization study, and the combined results resolve scattering consistent with a high temperature magnetic phase that persists above 600 K, reorients at the previously defined ${T}_{\text{AF}}=280$ K, and coexists with an electronic ground state whose phase behavior suggests the formation of a fluctuating charge or orbital phase that freezes below
Abstract: Through a neutron scattering, charge transport, and magnetization study, the correlated ground state in the bilayer iridium oxide Sr${}_{3}$Ir${}_{2}$O${}_{7}$ is explored. Our combined results resolve scattering consistent with a high temperature magnetic phase that persists above 600 K, reorients at the previously defined ${T}_{\text{AF}}=280$ K, and coexists with an electronic ground state whose phase behavior suggests the formation of a fluctuating charge or orbital phase that freezes below ${T}^{*}\ensuremath{\approx}70$ K. Our study provides a window into the emergence of multiple electronic order parameters near the boundary of the metal to insulator phase transition of the $5d$ ${J}_{\text{eff}}=1/2$ Mott phase.
TL;DR: Measurement of HTO and OBT activity concentration profiles in the subsurface 25 cm of soil suggests that O BT activity concentrations retained the signature of the historical tritium releases.
TL;DR: Cholesterol's molecular interactions with ether lipids as determined using a combination of small-angle neutron and X-ray scattering, and all-atom molecular dynamics simulations lend a better understanding of ether lipid-mediated cholesterol trafficking and the roles that the different lipid species have in determining the structural and dynamical properties of membrane associated biomolecules.
Abstract: Cholesterol and ether lipids are ubiquitous in mammalian cell membranes, and their interactions are crucial in ether lipid mediated cholesterol trafficking. We report on cholesterol's molecular interactions with ether lipids as determined using a combination of small-angle neutron and X-ray scattering, and all-atom molecular dynamics (MD) simulations. A scattering density profile model for an ether lipid bilayer was developed using MD simulations, which was then used to simultaneously fit the different experimental scattering data. From analysis of the data the various bilayer structural parameters were obtained. Surface area constrained MD simulations were also performed to reproduce the experimental data. This iterative analysis approach resulted in good agreement between the experimental and simulated form factors. The molecular interactions taking place between cholesterol and ether lipids were then determined from the validated MD simulations. We found that in ether membranes cholesterol primarily hydrogen bonds with the lipid headgroup phosphate oxygen, while in their ester membrane counterparts cholesterol hydrogen bonds with the backbone ester carbonyls. This different mode of interaction between ether lipids and cholesterol induces cholesterol to reside closer to the bilayer surface, dehydrating the headgroup's phosphate moiety. Moreover, the three-dimensional lipid chain spatial density distribution around cholesterol indicates anisotropic chain packing, causing cholesterol to tilt. These insights lend a better understanding of ether lipid-mediated cholesterol trafficking and the roles that the different lipid species have in determining the structural and dynamical properties of membrane associated biomolecules.
TL;DR: In this paper, inelastic neutron scattering is used to systematically investigate the Ni-doping evolution of low-energy spin excitations in BaFe2-xNixAs2 spanning from underdoped antiferromagnet to overdoped superconductor (0.03 <= x <= 0.18).
Abstract: We use inelastic neutron scattering to systematically investigate the Ni-doping evolution of the low-energy spin excitations in BaFe2-xNixAs2 spanning from underdoped antiferromagnet to overdoped superconductor (0.03 <= x <= 0.18). In the undoped state, BaFe2As2 changes from paramagnetic tetragonal phase to orthorhombic antiferromagnetic (AF) phase below about 138 K, where the low-energy (<=similar to 80 meV) spin waves form transversely elongated ellipses in the [H, K] plane of the reciprocal space. Upon Ni doping to suppress the static AF order and induce superconductivity, the c-axis magnetic exchange coupling is rapidly suppressed and the momentum distribution of spin excitations in the [H, K] plane is enlarged in both the transverse and longitudinal directions with respect to the in-plane AF ordering wave vector of the parent compound. As a function of increasing Ni-doping x, the spin excitation widths increase linearly but with a larger rate along the transverse direction. These results are in general agreement with calculations of dynamic susceptibility based on the random phase approximation (RPA) in an itinerant electron picture. For samples near optimal superconductivity at x approximate to 0.1, a neutron spin resonance appears in the superconducting state. Upon further increasing the electron doping to decrease the superconducting transition temperature T-c, the intensity of the low-energy magnetic scattering decreases and vanishes concurrently with vanishing superconductivity in the overdoped side of the superconducting dome. Comparing with the low-energy spin excitations centered at commensurate AF positions for underdoped and optimally doped materials (x <= 0.1), spin excitations in the overdoped side (x = 0.15) form transversely incommensurate spin excitations, consistent with the RPA calculation. Therefore, the itinerant electron approach provides a reasonable description to the low-energy AF spin excitations in BaFe2-xNixAs2.
TL;DR: In this article, the authors investigated a hematite bilayer film where the antiferromagnetic layer consisted of small hematites in the 2 to 16 nm range and found that a pronounced exchange bias effect occurred below the blocking temperature of 40 K.
Abstract: We investigated a hematite $\ensuremath{\alpha}$-Fe${}_{2}$O${}_{3}$/permalloy Ni${}_{80}$Fe${}_{20}$ bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the N\'eel temperature of bulk $\ensuremath{\alpha}$-Fe${}_{2}$O${}_{3}$ is known to be very high (860 K), we attribute the low-temperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5--1.0 ${\ensuremath{\mu}}_{B}$ per Fe atom within a depth of 1--2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains.
TL;DR: It is observed that a significant amount of the protein mass protrudes above the membrane, in contrast to the conjecture that all of the membrane-associated Bax states are umbrella-like, an effect reminiscent of the action of antimicrobial peptides on membranes.
TL;DR: Simulations and measurements show that, despite its shape, the device can be made to offer a near angular isotropic response to neutrons and that unfolded neutron spectra are in agreement with those obtained with a more traditional BSS.
Abstract: The design, simulation results and measurements of a new neutron energy spectrometer are presented. The device, which may be called NNS, for Nested Neutron Spectrometer, works under the same principles as a Bonner Sphere Spectrometer (BSS) System, i.e. whereby a thermal neutron detector is surrounded by a polyethylene moderator. However, the moderator is cylindrical in shape. The different thicknesses of moderator are created by inserting one cylinder into another, much like nested Russian dolls. This design results in a much lighter instrument that is also easier to use in the field. Simulations and measurements show that, despite its shape, the device can be made to offer a near angular isotropic response to neutrons and that unfolded neutron spectra are in agreement with those obtained with a more traditional BSS.
TL;DR: In this article, the effect of cooling rate subsequent to hot rolling on precipitate formation in the ferrite phase was investigated and it was shown that increasing the cooling rate prevents precipitate forming in the Ferrite phase at the cool deformation temperature.
TL;DR: An overview of the experiments that have been performed for both ground-based and space studies in an effort to characterise the response of these detectors to various particle types in low earth orbit is provided and results from the various space investigations are presented.
Abstract: A passive neutron-bubble dosemeter (BD), developed by Bubble Technology Industries, has been used for space applications. Both the bubble detector-personal neutron dosemeter and bubble detector spectrometer have been studied at ground-based facilities in order to characterise their response due to neutrons, heavy ion particles and protons. This technology was first used during the Canadian-Russian collaboration aboard the Russian satellite BION-9, and subsequently on other space missions, including later BION satellites, the space transportation system, Russian MIR space station and International Space Station. This paper provides an overview of the experiments that have been performed for both ground-based and space studies in an effort to characterise the response of these detectors to various particle types in low earth orbit and presents results from the various space investigations.
TL;DR: In this paper, microstructure, mechanical properties and residual stress were characterized along the cylinder bridge of engine blocks following thermal sand reclamation (TSR), T7 heat treatment, and service testing of the casting.
Abstract: The replacement of nodular cast iron with 319 type aluminum (Al) alloys in gasoline engine blocks is an example of the shift towards the use of lighter alloys in the automotive industry. However, excessive residual stress along the cylinder bore may lead to bore distortion, significantly reducing engine operating efficiency. In the current study, microstructure, mechanical properties and residual stress were characterized along the cylinder bridge of engine blocks following thermal sand reclamation (TSR), T7 heat treatment, and service testing of the casting. Neutron diffraction was effectively used to quantify the residual stress along both the Al cylinder bridge and the adjacent gray cast iron cylinder liners in the hoop, radial, and axial orientations with respect to the cylinder axis. The results suggest that an increase in cooling rate along the cylinder caused a significant refinement in microstructure at the bottom of the cylinder. In turn, this suggested an increase in alloy strength at the bottom of the cylinder relative to the top. This increased strength at the bottom of the cylinder likely reduced the susceptibility of the cylinder to rapid relief of residual stress at elevated temperature. In contrast, the coarse microstructure at the top of the cylinder likely triggered stress relief at an elevated temperature.
TL;DR: In this paper, inelastic neutron scattering was used to show that superconducting (SC) rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin excitations near the in-plane wave vector Q = (pi, 0) identical to that for iron arsenide superconductors.
Abstract: We use inelastic neutron scattering to show that superconducting (SC) rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin excitations near the in-plane wave vector Q = (pi, 0) identical to that for iron arsenide superconductors. Moreover, we find that these excitations change from incommensurate to commensurate with increasing energy and occur at the expense of spin waves associated with the coexisting root 5 x root 5 block AF phase. Since these spin excitations cannot come from Fermi surface nesting based on angle resolved photoemission experiments, our results indicate the presence of local moments in SC Rb0.82Fe1.68Se2 that may have a similar origin as the hourglass-like spin excitations in copper oxide superconductors.
TL;DR: Neutron-pair distribution function studies show that a brownmillerite-like model involving ordered vacancies and alternating octahedral and tetrahedral coordination at the metal sites, gives a better description of the local structure out to ∼5 Å.
Abstract: The local and average crystal structures and magnetic properties of the oxygen-deficient perovskite Sr2Fe1.5Cr0.5O5+y were studied using powder X-ray and neutron diffraction, neutron-pair distribution function analysis, and electron energy-loss spectroscopy. This material crystallizes in the cubic Pm3m space group, with a = 3.94491(14) A. The oxygen vacancies are distributed randomly throughout the perovskite-type structure, and the average coordination number of the Fe(Cr) sites is 5. Refinement of the neutron diffraction data indicates y ∼ 0.05. This is in discordance with an earlier report on a material with the same nominal composition and cell constant. Electron energy-loss Cr L2,3-edge spectroscopy shows that Cr3+ is present, which is also contrary to previous speculation. Neutron-pair distribution function studies show that a brownmillerite-like model involving ordered vacancies and alternating octahedral and tetrahedral coordination at the metal sites, gives a better description of the local stru...
TL;DR: In this article, the deuterium absorption and desorption of 55nm thick Mg films alloyed with Fe and Cr using in-situ neutron reflectometry was examined and it was shown that the catalytic effect of the Fe-Cr alloy is based on the avoidance of the formation of a blocking MgD 2 layer in the early stages of the absorption process.
TL;DR: In this paper, the influence of biaxiality of the loading on the crystallographic orientation dependence of crystal stress distributions is examined for polycrystalline solids deformed well into the elastoplastic regime.
Abstract: The influence of biaxiality of the loading on the crystallographic orientation dependence of crystal stress distributions is examined for polycrystalline solids deformed well into the elastoplastic regime. The examination is couched in terms of two decompositions of the stress. The first is a split of the tensor into its hydrostatic and deviatoric components; the second is a spectral decomposition of the deviatoric stress from which we express the relative values of the principal components as a function of the biaxiality of the stress. Using the framework provided by these decompositions, we investigate trends observed in the lattice strains in polycrystals subjected to biaxial loadings, comparing strains measured by neutron diffraction with finite element simulations. We conclude by showing how the orientation dependence of the stress distributions is influenced by the load biaxiality and by connecting features of the distributions to the elastic and plastic properties of the crystals. Implications of the results are discussed relative to the modeling of strain hardening and defect initiation.
TL;DR: In this article, the B-cation properties of 6 compounds with formula Sr2Fe1.9M0.1O5+y (M = Mn, Cr, Co; y = 0, 0.5) were synthesized in air and argon, exhibiting surprisingly different properties depending on the Bcation type in spite of the low doping level.
Abstract: Six compounds with formula Sr2Fe1.9M0.1O5+y (M = Mn, Cr, Co; y = 0, 0.5) were synthesized in air and argon, exhibiting surprisingly different properties depending on the B-cation type in spite of the low (5%) doping level. All argon synthesized phases, y ∼ 0, have long range brownmillerite ordering of oxygen vacancies with Icmm symmetry as shown by neutron diffraction (ND). All show long-range G-type antiferromagnetic order with Neel temperatures, TN, from variable temperature ND of 649(3)K, 636(2)K and 668(5)K for Cr, Mn and Co-compounds, respectively, compared with Sr2Fe2O5, TN = 693 K. Competing ferromagnetic interactions may be responsible for the anomalously low value in the M = Mn case. The air synthesized phases with y ∼ 0.5 show surprising variation with M as investigated by X-ray, TOF and constant wavelength neutron diffractions. The M = Co compound is isostructural with Sr4Fe4O11 (Sr2Fe2O5.5), Cmmm, while the M = Cr phase is cubic, Pm-3m, and that for M = Mn appears to be cubic but the reflections are systematically broadened in a manner which suggests a local Cmmm structure. NPDF studies show that the local structure of the Cr phase is better described in terms of a Cmmm ordering of oxygen vacancies with Fe–O coordination numbers of five and six. The M = Co material shows C-type antiferromagnetic long-range magnetic order at 4 K as found for Sr4Fe4O11. TN ∼ 230 K is inferred from a ZFC-FC magnetic susceptibility divergence compared with TN = 232 K for un-doped Sr4Fe4O11. The M = Cr and Mn compounds show no long-range magnetic ordering down to 4 K, but the divergence of ZFC and FC susceptibility data indicative of spin glass-like transitions occur at ∼60 K and ∼45 K for Cr and Mn, respectively. ND shows both diffuse and sharp Bragg magnetic reflections at positions consistent with a Cmmm cell for the M = Mn phase. For the M = Cr material, a very weak magnetic Bragg peak indexed as (1/2 1/2 1/2), consistent with a G-type AF order, is found at 4 K. These results rule out a spin glass-like ground state for both materials.
TL;DR: Air concentration data and ICRP dose coefficients were used to calculate inhalation committed effective doses (CED, E(50)) and thyroid equivalent doses (H) for adult members of the public and minor contributions to dose from the ingestion of contaminated food and water were not calculated.
TL;DR: In this paper, the authors used a combination of neutron reflectometry (NR), X-ray diffraction (XRD), and atomic force microscopy to elucidate the effects of alloying on the hydrogen storage properties of Mg at room temperature.
Abstract: Magnesium hydride has high storage capacity (7.6 wt % H) but very slow sorption kinetics. Addition of catalytic phases on the surface as well as alloying with transition metals is known to improve the properties. In this study, the sorption kinetics of a 50-nm Mg layer and Mg-10%Cr-10%V layer, capped with a CrV/Pd bilayer catalyst, are compared using a combination of neutron reflectometry (NR), X-ray diffraction (XRD), and atomic force microscopy to elucidate the effects of alloying on the hydrogen storage properties of Mg at room temperature. From NR it is found that the Cr–V alloyed layer shows both a delay in expansion in the first absorption cycle and a delay in contraction in the first desorption, which indicates a delay in nucleation of MgD2 and formation of substoichiometric MgD2-δ, respectively. Compared to pure Mg, the kinetics are strongly improved as no blocking MgD2 layer is formed. XRD showed a strong reduction in the Mg grain size for the Cr–V alloyed layer after one cycle. For pure Mg, the ...
TL;DR: In this paper, the authors used neutron inelastic scattering to characterize the acoustic phonons in the relaxor Pb(Mg${} 1/3}$Nb${} 2/3})O${} 3}$ (PMN) and demonstrate the presence of a highly anisotropic damping mechanism that is directly related to short-range polar correlations.
Abstract: We use neutron inelastic scattering to characterize the acoustic phonons in the relaxor Pb(Mg${}_{1/3}$Nb${}_{2/3}$)O${}_{3}$ (PMN) and demonstrate the presence of a highly anisotropic damping mechanism that is directly related to short-range polar correlations. For a large range of temperatures above ${T}_{c}\ensuremath{\sim}210$ K, where dynamic, short-range polar correlations are present, acoustic phonons propagating along [1$\overline{1}$0] and polarized along [110] (TA${}_{2}$ phonons) are overdamped and softened across most of the Brillouin zone. By contrast, acoustic phonons propagating along [100] and polarized along [001] (TA${}_{1}$ phonons) are overdamped and softened for a more limited range of wave vectors $q$. The anisotropy and temperature dependence of the acoustic phonon energy linewidth $\ensuremath{\Gamma}$ are directly correlated with neutron diffuse scattering cross section, indicating that polar nanoregions are the cause of the anomalous behavior. The damping and softening vanish for $q\ensuremath{\rightarrow}0$, i.e., for long-wavelength acoustic phonons near the zone center, which supports the notion that the anomalous damping is a result of the coupling between the relaxational component of the diffuse scattering and the harmonic TA phonons. Therefore, these effects are not due to large changes in the elastic constants with temperature because the elastic constants correspond to the long-wavelength limit. We compare the elastic constants we measure to those from Brillouin scattering experiments and to values reported for pure PbTiO${}_{3}$. We show that while the values of C${}_{44}$ are quite similar, those for C${}_{11}$ and C${}_{12}$ are significantly less in PMN and result in a softening of (C${}_{11}\ensuremath{-}{C}_{12}$) over PbTiO${}_{3}$. The elastic constants also show an increased elastic anisotropy [2C${}_{44}$/(C${}_{11}\ensuremath{-}{C}_{12}$)] in PMN versus that in PbTiO${}_{3}$. These results are suggestive of an instability to TA${}_{2}$ acoustic fluctuations in PMN and other relaxor ferroelectrics. We discuss our results in the context of the current debate over the ``waterfall'' effect and show that they are inconsistent with acoustic-optic phonon coupling or other models that invoke the presence of a second, low-energy optic mode.
TL;DR: The objective of this study was to provide the parameter values required to model OBT formation in the edible parts of plants following a hypothetical accidental tritium release to the atmosphere at night.
TL;DR: In this article, a structural analogue of the multiferroic Ba3NbFe3Si2O14 was synthesized and characterized using X-ray diffraction, magnetic susceptibility, specific heat, dielectric constant, and neutron diffraction.
Abstract: Polycrystalline Pb3TeCo3V2O14, a structural analogue of the multiferroic Ba3NbFe3Si2O14, was synthesized and characterized using X-ray diffraction, magnetic susceptibility, specific heat, dielectric constant, and neutron diffraction. Magnetic susceptibility, specific heat capacity measurements, and bond valence analysis confirmed that the V5+ ion is nonmagnetic, while Co2+ is in its high spin state (S = 3/2). Two magnetic transitions were seen at TN1 = 8.6 K and TN2 = 6.0 K where the spins first adopt a magnetic structure with propagation vector k = (0.752,0,1/2) and reorder into a commensurate structure with propagation vector k = (5/6,5/6,1/2). Changes in the dielectric constant at both magnetic phase transitions suggest that magnetoelectric coupling exists in Pb3TeCo3V2O14.