Dolor retrosternal en ni\uf1os y adolescentes

Este art\uedculo se enfoca en explorar el dolor retrosternal en ni\uf1os y adolescentes. Se revisan las causas frecuentes de este dolor y el m\ue9todo para su evaluaci\uf3n. Se pone especial hincapi\ue9 en las causas cardiacas de dolor retrostemal pedi\ue1trico, y en el modo en que puede diferenciarse de causas benignas m\ue1s frecuentes

The Impact of Cardiac Motion on Aortic Valve Flow Used in Computational Simulations of the Thoracic Aorta

Advancements in image-based computational modeling are producing increasingly more realistic representations of vasculature and hemodynamics, but so far have not compensated for cardiac motion when imposing inflow boundary conditions. The effect of cardiac motion on aortic flow is important when assessing sequelae in this region including coarctation of the aorta (CoA) or regurgitant fraction. The objective of this investigation was to develop a method to assess and correct for the influence of cardiac motion on blood flow measurements through the aortic valve (AoV) and to determine its impact on patient-specific local hemodynamics quantified by computational fluid dynamics (CFD). A motion-compensated inflow waveform was imposed into the CFD model of a patient with repaired CoA that accounted for the distance traveled by the basal plane during the cardiac cycle. Time-averaged wall shear stress (TAWSS) and turbulent kinetic energy (TKE) values were compared with CFD results of the same patient using the original waveform. Cardiac motion resulted in underestimation of flow during systole and overestimation during diastole. Influences of inflow waveforms on TAWSS were greatest along the outer wall of the ascending aorta (AscAo) (∼30 dyn/cm2). Differences in TAWSS were more pronounced than those from the model creation or mesh dependence aspects of CFD. TKE was slightly higher for the motion-compensated waveform throughout the aortic arch. These results suggest that accounting for cardiac motion when quantifying blood flow through the AoV can lead to different conclusions for hemodynamic indices, which may be important if these results are ultimately used to predict patient outcomes

p-type Bi₂ Se₃ for Topological Insulator and Low-Temperature Thermoelectric Applications

The growth and elementary properties of p-type Bi2Se3 single crystals are reported. Based on a hypothesis about the defect chemistry of Bi2Se3, the p-type behavior has been induced through low-level substitutions (1% or less) of Ca for Bi. Scanning tunneling microscopy is employed to image the defects and establish their charge. Tunneling and angle-resolved photoemission spectra show that the Fermi level has been lowered into the valence band by about 400 meV in Bi1.98Ca0.02Se3 relative to the n-type material. p-type single crystals with ab-plane Seebeck coefficients of +180 μV/K at room temperature are reported. These crystals show an anomalous peak in the Seebeck coefficient at low temperatures, reaching +120 μV K-1 at 7 K, giving them a high thermoelectric power factor at low temperatures. In addition to its interesting thermoelectric properties, p-type Bi2Se3 is of substantial interest for studies of technologies and phenomena proposed for topological insulators

Site Assignment for Copper Nuclear-Quadrupole-Resonance Lines in YBa2Cu3O7

Data on the Cu63 nuclear-magnetic-resonance intensity in powdered ceramic samples of YBa2Cu3O7 are analyzed to yield the relative and absolute intensities of the Cu(1) and Cu(2) sites, using similar data on Cu63 in Cu2O as a reference standard. These data confirm the assignment of the 31.48 MHz nuclear-quadrupole-resonance line to the Cu(2) (planar) sites and the 22.05 MHz line to the Cu(1) (chain) sites mandated by recent experiments at other laboratories. Relaxation data for Y89, also presented, may reflect antiferromagnetically correlated spin fluctuations in the planes

Anisotropic Nuclear Relaxation in YBa2Cu3O7

Data are presented for the magnetic susceptibility of YBa2Cu3O7 and for the anisotropy of the copper nuclear spin-lattice relaxation time T1 in the normal state for planar [Cu(2)] sites in this system. Using the Cu NMR shift to partition the susceptibility and estimate the density of states, we analyze the conventional enhanced Korringa model of T1 contributions, finding it incapable of accounting for the anisotropy of the observed relaxation times. A localized spin-fluctuation picture is also discussed briefly

Magnetic Penetration Depth in Single-Crystal YBa2Cu3O7-

We report the first measurement of the magnetic penetration depth (T,) in single crystals of YBa2Cu3O7- (0.1). Results are consistent with conventional s-wave pairing, and yield penetration depths of ab(0)=141530 and c(0)\u3e7000, parallel and perpendicular to the basal plane, respectively. Comparative data on sintered YBa2Cu3O7 are also shown to be consistent with the single-crystal results. The muon-spin-rotation data, together with specific-heat results, indicate a two-dimensional carrier density of 2D8×1014 carriers cm-2 and a basal-plane effective mass of mab*me10

Computational simulations demonstrate altered wall shear stress in aortic coarctation patients treated by resection with end-to-end anastomosis.

International audienceBACKGROUND: Atherosclerotic plaque in the descending thoracic aorta (dAo) is related to altered wall shear stress (WSS) for normal patients. Resection with end-to-end anastomosis (RWEA) is the gold standard for coarctation of the aorta (CoA) repair, but may lead to altered WSS indices that contribute to morbidity. METHODS: Computational fluid dynamics (CFD) models were created from imaging and blood pressure data for control subjects and age- and gender-matched CoA patients treated by RWEA (four males, two females, 15 ± 8 years). CFD analysis incorporated downstream vascular resistance and compliance to generate blood flow velocity, time-averaged WSS (TAWSS), and oscillatory shear index (OSI) results. These indices were quantified longitudinally and circumferentially in the dAo, and several visualization methods were used to highlight regions of potential hemodynamic susceptibility. RESULTS: The total dAo area exposed to subnormal TAWSS and OSI was similar between groups, but several statistically significant local differences were revealed. Control subjects experienced left-handed rotating patterns of TAWSS and OSI down the dAo. TAWSS was elevated in CoA patients near the site of residual narrowings and OSI was elevated distally, particularly along the left dAo wall. Differences in WSS indices between groups were negligible more than 5 dAo diameters distal to the aortic arch. CONCLUSIONS: Localized differences in WSS indices within the dAo of CoA patients treated by RWEA suggest that plaque may form in unique locations influenced by the surgical repair. These regions can be visualized in familiar and intuitive ways allowing clinicians to track their contribution to morbidity in longitudinal studies

Magnetic-field-induced shift of the optical band gap in Ni3 V2 O8

Physical Review B - Condensed Matter and Materials Physics. Volume 89, Issue 16, 17 April 2014, Article number 165120.We employ a magnetic-field driven antiferromagnetic to the fully polarized state transition in Ni3V2O8 to investigate the interaction between spin ordering and driven charge excitations, with special emphasis on the color properties. Our measurements reveal field-induced blue shifts of the band gap that are much larger than that of the Zeeman effect in isolation, anticipating a more greenish appearance in the fully polarized state. This color change is verified with direct photographic images and emanates from charge density differences around the Ni and O centers in high fields. © 2014 American Physical Society