149 research outputs found
Simple Patient-Based Transmantle Pressure and Shear Estimate From Cine Phase-Contrast MRI in Cerebral Aqueduct
From measurements of the oscillating flux of the cerebrospinal fluid (CSF) in the aqueduct of Sylvius, we elaborate a
patient-based methodology for transmantle pressure (TRP) and
shear evaluation. High-resolution anatomical magnetic resonance imaging first permits a precise 3-D anatomical digitalized reconstruction of the Sylvius’s aqueduct shape. From this, a very fast approximate numerical flow computation, nevertheless consistent with analytical predictions, is developed. Our approach includes
the main contributions of inertial effects coming from the pulsatile flow and curvature effects associated with the aqueduct bending. Integrating the pressure along the aqueduct longitudinal center-line enables the total dynamic hydraulic admittances of the aqueduct to be evaluated, which is the pre-eminent contribution to the
CSF pressure difference between the lateral ventricles and the subarachnoidal spaces also called the TRP. The application of the method to 20 healthy human patients validates the hypothesis of the proposed approach and provides a first database for normal aqueduct CSF flow. Finally, the implications of our results for modeling
and evaluating intracranial cerebral pressure are discussed
Valence Instability of YbCuSi through its quantum critical point
We report Resonant inelastic x-ray scattering measurements (RIXS) in
YbCuSi at the Yb L edge under high pressure (up to 22 GPa) and at
low temperatures (down to 7 K) with emphasis on the vicinity of the transition
to a magnetic ordered state. We find a continuous valence change towards the
trivalent state with increasing pressure but with a pronounced change of slope
close to the critical pressure. Even at 22 GPa the Yb state is not fully
achieved. The pressure where this feature is observed decreases as the
temperature is reduced to 9 GPa at 7K, a value close to the critical pressure
(\itshape{p\normalfont{}}\normalfont 7.5 GPa) where magnetic
order occurs. The decrease in the valence with decreasing temperature
previously reported at ambient pressure is confirmed and is found to be
enhanced at higher pressures. We also compare the f electron occupancy between
YbCuSi and its Ce-counterpart, CeCuSi
Observation of Magnetic Order in a Superconductor
Polarized beam neutron scattering measurements on a highly perfect crystal of
show a distinct magnetic transition with an onset at
about 235K, the temperature expected for the pseudogap transition. The moment
is found to be about 0.1 for each sublattice and have a correlation
length of at least 75 \AA. We found the critical exponent for the magnetic
neutron intensity to be 2 =0.37 0.12. This is the proper range for
the class of transition that has no specific heat divergence possibly
explaining why none is found at the pseudogap transition.Comment: 3 figure
2D orbital-like magnetic order in
In high temperature copper oxides superconductors, a novel magnetic order
associated with the pseudogap phase has been identified in two different
cuprate families over a wide region of temperature and doping. We here report
the observation below 120 K of a similar magnetic ordering in the archetypal
cuprate (LSCO) system for x=0.085. In contrast to the
previous reports, the magnetic ordering in LSCO is {\it\bf only} short range
with an in-plane correlation length of 10 \AA\ and is bidimensional
(2D). Such a less pronounced order suggests an interaction with other
electronic instabilities. In particular, LSCO also exhibits a strong tendency
towards stripes ordering at the expense of the superconducting state.Comment: 4 figures, submitted to Phys. Rev. Let
Biomechanical modeling and Magnetic Resonance Imaging to investigate CSF flow physiology
Nowadays Phase contrast Magnetic Resonance Imaging (PC-MRI) is the only sensor able to measure in physiological conditions blood and cerebrospinal fluids (CSF) flow dynamics during cardiac cycle at different levels of the craniospinal system [1]. Combining modelling and in Vivo PC-MRI measurments of CSF Flow at the cervical Spinal (Qs) and Aqueduct of Sylvius (Qv) or Sub-Arachnoidal cerebral (Qc) levels makes it possible to compute Intracranial pressure (ICP) as well as get a deep insight into the LCS dynamical system. Inertia has been neglected in most of previous LCS models. Our simple model show that inertia plays a crucial role in particular in the optimal LCS flow amplitudes and phases
Purely antiferromagnetic frustrated Heisenberg model in spin ladder compound BaFeSe
The spin dynamics in the block magnetic phase of the iron-based ladder
compound \bfs\ has been studied by means of single crystal inelastic neutron
scattering. Using linear spin wave theory and Monte-Carlo simulations, our
analysis points to a magnetic Heisenberg model with effective frustrated
antiferromagnetic couplings only, able to describe both the exotic block order
and its dynamics. This new and purely antiferromagnetic picture offers a
fruitful perspective to describe multiferroic properties but also understand
the origin of the stripe-like magnetic instability observed under pressure as
well as in other parent compounds with similar crystalline structure
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