118 research outputs found
High-frequency dynamics in the near-surface region studied by inelastic x-ray scattering: The case of liquid indium
Inelastic x-ray scattering in grazing angle geometry provides a novel tool for studying the surface and bulk lattice dynamics in a single experiment by varying the incidence angle around the critical angle of total reflection. At very small incidence angles (below the critical angle), it is possible to study the collective dynamics in a subsurface region of a few nanometres at interatomic length and time scales. An experimental study on liquid indium in the near-surface region is presented here and the results are analysed within a theoretical framework, based on classical hydrodynamics for the height-height fluctuations (capillary waves and non-propagating fluctuations) and generalized hydrodynamics for the bulk density fluctuations. The investigation reveals the presence of capillary waves in the inelastic x-ray spectra as an additional contribution at zero-energy transfer and a modification of the bulk density fluctuation contribution. A longer structural relaxation time and a larger longitudinal viscosity with respect to bulk indium are observed, similarly to related studies in confined liquids. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Blockchain for the circular economy: Theorizing blockchain\u27s role in the transition to a circular economy through an empirical investigation
Blockchain is increasingly lauded as an enabler of the transition to a circular economy. While there is considerable conceptual research and some empirical studies on this phenomenon, scholars have yet to develop a theoretical model of blockchain\u27s role in this transition. Grounded in the sustainability transition literature, this paper addresses this gap through the following research question: What role does blockchain play in the transition to a circular economy? Following an abductive approach, we conducted interviews with ground-level experts implementing blockchain innovations for the circular economy across Europe and the United States. Through a thematic analysis, we derived a theoretical model of the relationships among (1) drivers and barriers of the transition to a circular economy, (2) blockchain innovation for the circular economy, (3) technical challenges of blockchain, and (4) the circular economy. While blockchain plays a moderating role, interviewees considered it only an infrastructural resource rather than a panacea
In-between Bragg reflections: Thermal diffuse scattering and vibrational spectroscopy with x-rays
In the last decade diffuse scattering studies re-gained their place in the domain of lattice dynamics studies. The use of thermal diffuse scattering becomes particularly efficient when coupled with vibrational spectroscopy, where inelastic x-ray scattering can be advantageous compared to inelastic neutron scattering, and state-of-the-art ab initio calculations. We present a brief summary of the experimental and theoretical background, give an overview of the principal experimental implementations, and discuss a representative set of examples of such a combined approach
High-frequency subsurface and bulk dynamics of liquid indium
We have performed bulk and surface-sensitive inelastic x-ray scattering experiments on liquid indium with 3 meV energy resolution. The experimental data are well reproduced within a generalized hydrodynamic model including structural and microscopic relaxation processes. We find a longitudinal viscosity of 22 mPa s in the near-surface region compared to 7.4 mPa s in the bulk. The origin of the increase is associated with a slowing down of the collective dynamics in a subsurface region of 4.6 nm. © 2007 The American Physical Society
Lattice dynamics of MgSiO perovskite (bridgmanite) studied by inelastic x-ray scattering and ab initio calculations
We have determined the lattice dynamics of MgSiO perovskite (bridgmanite)
by a combination of single-crystal inelastic x-ray scattering and ab initio
calculations. We observe a remarkable agreement between experiment and theory,
and provide accurate results for phonon dispersion relations, phonon density of
states and the full elasticity tensor. The present work constitutes an
important milestone to extend this kind of combined studies to extreme
conditions of pressure and temperature, directly relevant for the physics and
the chemistry of Earth's lower mantle
Lattice dynamics of coesite
The lattice dynamics of coesite has been studied by a combination of diffuse x-ray scattering, inelastic x-ray scattering and ab initio lattice dynamics calculations. The combined technique gives access to the full lattice dynamics in the harmonic description and thus eventually provides detailed information on the elastic properties, the stability and metastability of crystalline systems. The experimentally validated calculation was used for the investigation of the eigenvectors, mode character and their contribution to the density of vibrational states. High-symmetry sections of the reciprocal space distribution of diffuse scattering and inelastic x-ray scattering spectra as well as the density of vibrational states and the dispersion relation are reported and compared to the calculation. A critical point at the zone boundary is found to contribute strongly to the main peak of the low-energy part in the density of vibrational states. Comparison with the most abundant SiO2 polymorph - α-quartz - reveals similarities and distinct differences in the low-energy vibrational properties
Terahertz electric-field driven dynamical multiferroicity in SrTiO
The emergence of collective order in matter is among the most fundamental and
intriguing phenomena in physics. In recent years, the ultrafast dynamical
control and creation of novel ordered states of matter not accessible in
thermodynamic equilibrium is receiving much attention. Among those, the
theoretical concept of dynamical multiferroicity has been introduced to
describe the emergence of magnetization by means of a time-dependent electric
polarization in non-ferromagnetic materials. In simple terms, a large amplitude
coherent rotating motion of the ions in a crystal induces a magnetic moment
along the axis of rotation. However, the experimental verification of this
effect is still lacking. Here, we provide evidence of room temperature
magnetization in the archetypal paraelectric perovskite SrTiO due to this
mechanism. To achieve it, we resonantly drive the infrared-active soft phonon
mode with intense circularly polarized terahertz electric field, and detect a
large magneto-optical Kerr effect. A simple model, which includes two coupled
nonlinear oscillators whose forces and couplings are derived with ab-initio
calculations using self-consistent phonon theory at a finite temperature,
reproduces qualitatively our experimental observations on the temporal and
frequency domains. A quantitatively correct magnitude of the effect is obtained
when one also considers the phonon analogue of the reciprocal of the Einsten -
de Haas effect, also called the Barnett effect, where the total angular
momentum from the phonon order is transferred to the electronic one. Our
findings show a new path for designing ultrafast magnetic switches by means of
coherent control of lattice vibrations with light.Comment: Main text: 10 pages, 4 figures, methods and 8 supplemental figure
X-ray Observations and Infrared Identification of the Transient 7.8 s X-ray Binary Pulsar XTE J1829-098
XMM-Newton and Chandra observations of the transient 7.8 s pulsar XTE
J1829-098 are used to characterize its pulse shape and spectrum, and to
facilitate a search for an optical or infrared counterpart. In outburst, the
absorbed, hard X-ray spectrum with Gamma = 0.76+/-0.13 and N_H = (6.0+/-0.6) x
10^{22} cm^{-2} is typical of X-ray binary pulsars. The precise Chandra
localization in a faint state leads to the identification of a probable
infrared counterpart at R.A. = 18h29m43.98s, decl. = -09o51'23.0" (J2000.0)
with magnitudes K=12.7, H=13.9, I>21.9, and R>23.2. If this is a highly
reddened O or B star, we estimate a distance of 10 kpc, at which the maximum
observed X-ray luminosity is 2x10^{36} ergs s^{-1}, typical of Be X-ray
transients or wind-fed systems. The minimum observed luminosity is
3x10^{32}(d/10 kpc)^2 ergs s^{-1}. We cannot rule out the possibility that the
companion is a red giant. The two known X-ray outbursts of XTE J1829-098 are
separated by ~1.3 yr, which may be the orbital period or a multiple of it, with
the neutron star in an eccentric orbit. We also studied a late M-giant
long-period variable that we found only 9" from the X-ray position. It has a
pulsation period of ~1.5 yr, but is not the companion of the X-ray source.Comment: 6 pages, 7 figures. To appear in The Astrophysical Journa
Crystal Growth with Oxygen Partial Pressure of the BaCuSi2O6 and Ba1-xSrxCuSi2O6 Spin Dimer Compounds
BaCuSi2O6 is a quasi-two-dimensional spin dimer system and a model material for studying Bose-Einstein condensation (BEC) of magnons in high magnetic fields. The new Bai(1-x)Sr(x)CuSi(2)O(6) mixed system, which can be grown with x <= 0.3, and BaCuSi2O6, both grown by using a crystal growth method with enhanced oxygen partial pressure, have the same tetragonal structure (I4(1)/acd) at room temperature. The mixed system shows no structural phase transition so that the tetragonal structure is stable down to low temperatures. The oxygen partial pressure acts as a control parameter for the growth process. A detailed understanding of the crystal structure depending on the oxygen content will enable the study of the spin dynamics of field-induced order states in this model magnetic compound of high current interest with only one type of dimer layers, which shows the same distance between the Cu atoms, in the structure
Lattice dynamics of α-cristobalite and the Boson peak in silica glass
The lattice dynamics of the silica polymorph {\alpha}-cristobalite has been
investigated by a combination of diffuse and inelastic x-ray scattering and ab
initio lattice dynamics calculations. Phonon dispersion relations and
vibrational density of states are reported and the phonon eigenvectors analysed
by a detailed comparison of scattering intensities. The experimentally
validated calculation is used to identify the vibration contributing most to
the first peak in the density of vibrational states. The comparison of its
displacement pattern to the silica polymorphs {\alpha}-quartz and coesite and
to vitreous silica reveals a distinct similarity and allows for decisive
conclusions on the vibrations causing the so-called Boson peak in silica glass
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