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 YbCu2_2Si2_2 through its quantum critical point

We report Resonant inelastic x-ray scattering measurements (RIXS) in YbCu$_2$Si$_2$ at the Yb L$_{3}$ 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$^{+3}$ 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{$_c$}}\normalfont $\approx$ 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 YbCu$_2$Si$_2$ and its Ce-counterpart, CeCu$_2$Si$_2$

Observation of Magnetic Order in a YBa2Cu3O6.6{\rm YBa_2Cu_3O_{6.6}} Superconductor

Polarized beam neutron scattering measurements on a highly perfect crystal of ${\rm YBa_2Cu_3O_{6.6}}$ 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 $\mu_B$ 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$\beta$ =0.37$\pm$ 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 La2−xSrxCuO4{\rm La_{2-x}Sr_xCuO_4}

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 ${\rm La_{2-x}Sr_xCuO_4}$ (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 $\sim$ 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 BaFe2_2Se3_3

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