1,241 research outputs found
Definition of anatomical zero positions for assessing shoulder pose with 3D motion capture during bilateral abduction of the arms
Background: Surgical interventions at the shoulder may alter function of the shoulder complex. Clinically, the outcome can be assessed by universal goniometry. Marker-based motion capture may not resemble these results due to differing angle definitions. Methods: The clinical inspection of bilateral arm abduction for assessing shoulder dysfunction is performed with a marker based 3D optical measurement method. An anatomical zero position of shoulder pose is proposed to determine absolute angles according to the Neutral-0-Method as used in orthopedic context. Static shoulder positions are documented simultaneously by 3D marker tracking and universal goniometry in 8 young and healthy volunteers. Repetitive bilateral arm abduction movements of at least 150° range of motion are monitored. Similarly a subject with gleno-humeral osteoarthritis is monitored for demonstrating the feasibility of the method and to illustrate possible shoulder dysfunction effects. Results: With mean differences of less than 2°, the proposed anatomical zero position results in good agreement between shoulder elevation/depression angles determined by 3D marker tracking and by universal goniometry in static positions. Lesser agreement is found for shoulder pro-/retraction with systematic deviations of up to 6°. In the bilateral arm abduction movements the volunteers perform a common and specific pattern in clavicula-thoracic and gleno-humeral motion with maximum shoulder angles of 32° elevation, 5° depression and 45° protraction, respectively, whereas retraction is hardly reached. Further, they all show relevant out of (frontal) plane motion with anteversion angles of 30° in overhead position (maximum abduction). With increasing arm anteversion the shoulder is increasingly retroverted, with a maximum of 20° retroversion. The subject with gleno-humeral osteoarthritis shows overall less shoulder abduction range of motion but with increased out-of-plane movement during abduction. Conclusions: The proposed anatomical zero definition for shoulder pose fills the missing link for determining absolute joint angles for shoulder elevation/depression and pro-/retraction. For elevation-/depression the accuracy suits clinical expectations very well with mean differences less than 2° and limits of agreement of 8.6° whereas for pro-/retraction the accuracy in individual cases may be inferior with limits of agreement of up to 24.6°. This has critically to be kept in mind when applying this concept to shoulder intervention studies
Dust Stratification in Young Circumstellar Disks
We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S,
RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO,
and C18O as well as broad emission lines of gas phase12CO. The narrow
absorption lines of CO are shown to originate from the colder circumstellar
gas. We find that the line of sight gas column densities resulting from the CO
absorption lines are much higher than expected for the measured extinction for
each source and suggest the gas to dust ratio is measuring the dust settling
and/or grain coagulation in these extended disks. We provide a model of
turbulence, dust settling and grain growth to explain the results. The
techniques presented here allow us to provide some observationally-motivated
bounds on accretion disk alpha in protostellar systems
(2,4,6-Trimethylphenyl)boronic acid–triphenylphosphine oxide (1/1)
In the crystal structure of the title compound, C9H13BO2·C18H15OP, there are O—H⋯O hydrogen bonds between the O atom of triphenylphosphine oxide and one hydroxy group of the boronic acid. Boronic acid molecules form inversion-related hydrogen-bonded dimers in an R
2
2(8) motif. The structure is consolidated by intermolecular C—H⋯O bonds and C—H⋯π interactions
Energy dissipation in the time domain governed by bosons in a correlated material
In complex materials various interactions play important roles in determining
the material properties. Angle Resolved Photoelectron Spectroscopy (ARPES) has
been used to study these processes by resolving the complex single particle
self energy and quantifying how quantum interactions modify bare
electronic states. However, ambiguities in the measurement of the real part of
the self energy and an intrinsic inability to disentangle various contributions
to the imaginary part of the self energy often leave the implications of such
measurements open to debate. Here we employ a combined theoretical and
experimental treatment of femtosecond time-resolved ARPES (tr-ARPES) and show
how measuring the population dynamics using tr-ARPES can be used to separate
electron-boson interactions from electron-electron interactions. We demonstrate
the analysis of a well-defined electron-boson interaction in the unoccupied
spectrum of the cuprate BiSrCaCuO characterized by an
excited population decay time constant that maps directly to a
discrete component of the equilibrium self energy not readily isolated by
static ARPES experiments.Comment: 19 pages with 6 figure
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Ultrafast modulation of the chemical potential in BaFe2As2 by coherent phonons
Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in BaFe2As2 around the high-symmetry points Γ and M. A global oscillation of the Fermi level at the frequency of the A1g(As) phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the A1g(As) phonon mode combined with a low electron diffusivity perpendicular to the layers. The results establish a novel way to tune the electronic properties of iron pnictides: coherent control of the effective chemical potential. The results further suggest that the equilibration time for the effective chemical potential needs to be considered in the ultrafast electronic structure dynamics of materials with weak interlayer coupling. © 2014 American Physical Society
Coherent excitations and electron phonon coupling in Ba/EuFe_2As_2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy
We employed femtosecond time- and angle-resolved photoelectron spectroscopy
to analyze the response of the electronic structure of the 122 Fe-pnictide
parent compounds Ba/EuFe_2As_2 and optimally doped BaFe_{1.85}Co_{0.15}As_2
near the \Gamma point to femtosecond optical excitation. We identify pronounced
changes of the electron population within several 100 meV above and below the
Fermi level, which we explain as combination of (i) coherent lattice
vibrations, (ii) a hot electron and hole distribution, and (iii) transient
modifications of the chemical potential. The response of the three different
materials is very similar. In the Fourier transformation of the time-dependent
photoemission intensity we identify three modes at 5.6, 3.3, and 2.6 THz. While
the highest frequency mode is safely assigned to the A_{1g} mode, the other two
modes require a discussion in comparison to literature. The time-dependent
evolution of the hot electron distribution follows a simplified description of
a transient three temperature model which considers two heat baths of lattice
vibrations, which are more weakly and strongly coupled to transiently excited
electron population. Still the energy transfer from electrons to the strongly
coupled phonons results in a rather weak, momentum-averaged electron-phonon
coupling quantified by values for \lambda between 30 and 70 meV^2.
The chemical potential is found to present a transient modulation induced by
the coherent phonons. This change in the chemical potential is particularly
strong in a two band system like in the 122 Fe-pnictide compounds investigated
here due to the pronounced variation of the electrons density of states close
to the equilibrium chemical potential.Comment: 10 pages, 6 figure
Coherent Modulation of Quasiparticle Scattering Rates in a Photoexcited Charge-Density-Wave System
We present a complementary experimental and theoretical investigation of relaxation dynamics in the charge-density-wave (CDW) system TbTe3 after ultrafast optical excitation. Using time- and angle-resolved photoemission spectroscopy, we observe an unusual transient modulation of the relaxation rates of excited photocarriers. A detailed analysis of the electron self-energy based on a nonequilibrium Green's function formalism reveals that the phase space of electron-electron scattering is critically modulated by the photoinduced collective CDW excitation, providing an intuitive microscopic understanding of the observed dynamics
Persistent order due to transiently enhanced nesting in an electronically excited charge density wave
Non-equilibrium conditions may lead to novel properties of materials with
broken symmetry ground states not accessible in equilibrium as vividly
demonstrated by non-linearly driven mid-infrared active phonon excitation.
Potential energy surfaces of electronically excited states also allow to
direct nuclear motion, but relaxation of the excess energy typically excites
fluctuations leading to a reduced or even vanishing order parameter as
characterized by an electronic energy gap. Here, using femtosecond time- and
angle-resolved photoemission spectroscopy, we demonstrate a tendency towards
transient stabilization of a charge density wave after near-infrared
excitation, counteracting the suppression of order in the non-equilibrium
state. Analysis of the dynamic electronic structure reveals a remaining energy
gap in a highly excited transient state. Our observation can be explained by a
competition between fluctuations in the electronically excited state, which
tend to reduce order, and transiently enhanced Fermi surface nesting
stabilizing the order
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