489 research outputs found
Geothermal Heat Flux and its Influence on the Oceanic Abyssal Circulation and Radiocarbon Distribution
Cross sections for the excitation of isovector charge-exchange resonances in 208Tl
The Glauber approximation for the treatment of heavy-ion scattering, has
already been shown to give reliable predictions for the reaction cross section
in the particular case of intermediate energy charge-exchange processes. In the
present work, we couple a Glauber-type model to microscopic Random Phase
Approximation calculations of the charge-exchange excitations of Pb.
The aim is to solve the longstanding question whether the very elusive
charge-exchange isovector monopole has been really identified in the past
experiments, or other multipoles were prevalent in the observed spectra.Comment: text + 4 figures; accepted for publication in Phys. Rev.
Active and reactive power control based on predictive voltage control in a six-phase generation system using modular matrix converters
Geothermal heating in the Panama Basin. Part II: abyssal water mass transformation
Diabatic upwelling of abyssal waters is investigated in the Panama Basin employing the water mass transformation framework of Walin [1982]. We find that, in large areas of the basin, the bottom boundary layer is very weakly stratified and extends hundreds of meters above the sea floor. Within the weakly stratified bottom boundary layer (wsBBL) neutral density layers intercept the bottom of the basin. The area of these density layer incrops increases gradually as the abyssal waters become lighter. Large incrop areas are associated with strong diabatic upwelling of abyssal water, geothermal heating being the largest buoyancy source. While a significant amount of water mass transformation is due to extreme turbulence downstream of the Ecuador Trench, the only abyssal water inflow passage, water mass transformation across the upper boundary of abyssal water layer is accomplished almost entirely by geothermal heating
Geothermal heating in the Panama Basin. Part I: hydrography of the basin
The Panama Basin serves as a laboratory to investigate abyssal water upwelling. The basin has only a single abyssal water inflow pathway through the narrow Ecuador Trench. The estimated critical inflow through the Trench reaches 0.34â±â0.07 m sâ1, resulting in an abyssal water volume inflow of 0.29â±â0.07 Sv. The same trench carries the return flow of basin waters that starts just 200 m above the bottom and is approximately 400 m deeper than the depth of the next possible deep water exchange pathway at the Carnegie Ridge Saddle. The curvature of temperatureâsalinity diagrams is used to differentiate the effect of geothermal heating on the deep Panama Basin waters that was found to reach as high as 2200 m depth, which is about 500 m above the upper boundary of the abyssal water layer
The weakly stratified bottom boundary layer of the global ocean
The weakly stratified bottom boundary layer (wsBBL) of the global ocean is currently unmapped; even the definition of the wsBBL layer is yet lacking. However, recent studies point to the wsBBL as a region where most of the abyssal water transformation takes place. In this study, historical highâresolution density profiles are used to map the properties of the wsBBL in the global ocean. We use a density gradient criteria ( urn:x-wiley:21699275:media:jgrc22951:jgrc22951-math-0001 kg mâ 4) to define the top of the layer. The thickness of the wsBBL varies from several meters to over a thousand meters and can be used as a rule of thumb to differentiate basin walls from the basin bottom, respectively. Although the thickness varies greatly, the pressure at the top of the wsBBL varies relatively smoothly allowing us to map its distribution across the ocean along with the density of the wsBBL. The neutral density, ÎłwsBBL, and pressure, PwsBBL, of the upper boundary of the wsBBL are highly correlated within each ocean basin. Diagrams of ÎłwsBBL versus PwsBBL clearly differentiate the different basins, connected by the narrow channels, along the pathways of abyssal water circulation. The diagrams give insight into the different mechanisms of abyssal water transformation and highlight locations where transformation happens: interâbasin channels and over some parts of midâoceanic ridges such as found in the Brazil Basin, in the Guiana Basin, and in the Southwest Pacific Basin
His-Bundle Pacing in a Patient With Tricuspid and Mitral Prosthetic Valves Without Suitable Coronary Veins for Lead Placement
Atrioventricular block in patients with a prosthetic tricuspid valve and a pacemaker with a dysfunctional epicardial lead is not uncommon. In such instances, coronary sinus lead placement is the preferred option, but it has a failure rate of 10%-15%. An atrial transseptal left ventricular lead placement has been proposed as an alternative, but this approach is not feasible in patients with a prosthetic mitral valve. This analysis represents the first reported case of His-bundle pacing from the atria in a patient with prosthetic tricuspid and mitral valves, with no suitable coronary veins for lead placement. © 2021 The Author
Depolarization-repolarization synchrony after right ventricular and left bundle branch area pacing
Introduction: Left bundle branch area pacing (LBBAP) has been recently proposed to overcome the limitations associated with right ventricular pacing (RVP) and has been suggested as a new physiological pacing form with high feasibility and safety. A greater difference between QRS complex and T-wave angle directions has been proposed as a marker of abnormal electrical activity in several patient populations, but a comparison between these two pacing modalities has never been performed. The total cosine R to T (TCRT) is an ECG descriptor that accounts for depolarization-repolarization synchrony by measuring the difference between their directions. The purpose of this study was to compare TCRT in patients referred for RVP and LBBAP pacing as anti-bradycardia therapy.
Methods: ECG recordings from 134 patients (82 LBBAP, 52 RVP) were classified into two groups, narrow QRS and wide QRS, depending on the patientâs QRS duration prior to implantation. In the post-implantation state, the TCRT index was calculated from a median beat calculated for each patient. Singular value decomposition was applied to the median beat in the eight independent ECG leads (I, II, V1, V2, V3, V4, V5, V6). The QRS complex and T wave loops in a three-dimensional space were determined from the first three components of the decomposition. TCRT was computed as the average of the cosines of the angles between the QRS complex directions and the maximum T wave direction. More positive values corresponded to more synchronized depolarization and repolarization processes while more negative values indicated larger differences in the orientation of the QRS and T wave loops and, therefore, greater dyssynchronization.
Results: showed that TCRT took negative values for both techniques, RVP and LBBAP, and both groups, narrow and wide QRS, indicating that pacing generated dyssynchronization between ventricular depolarization and repolarization. Nevertheless, TCRT values for both groups were significantly more negative (p<0.01) for RVP than for LBBAP. We hypothesize that cardiac memory induced by pacing could account for these negative TCRT values. In any case, LBBAP did not increase the difference in the QRS complex and T wave loop orientations as much as RVP.
Conclusion: LBBAP induces less dyssynchrony than RVP in the depolarization-repolarization process
Electrical properties of stoichiometric BiFeO3 prepared by mechanosynthesis with either conventional or spark plasma sintering
Phase-pure powders of stoichiometric BiFeO3 have been prepared by mechanosynthesis. Ceramics sintered by either conventional heating in air or spark plasma sintering (SPS) followed by oxidative anneal in air are highly insulating with conductivity e.g. ~10â6 Scmâ1 at 300 °C and activation energy 1.15(2) eV, which are comparable to those of a good-quality BiFeO3 single crystal. By contrast, the as-prepared SPS sample without the post-sinter anneal shows higher conductivity e.g. ~10â6 Scmâ1 at 225 °C and lower activation energy 0.67(3) eV, indicating some reduction of the sample by the SPS process. The reason for the high conductivity observed in some ceramic samples reported in the literature appears to be unclear at presentGobierno de España CTQ 2011-27626 MAT 2008-06619Junta de Andalucia TEP-0300
Thermal characterization of Montmorillonite clays saturated with various cations
Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li+, Cs+, NH 4 +, Mg2+ and Al3+. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, ÎE. Decreases in c-axis basal spacing (d 001) values determined from XRD patterns for the different montmorillonite samples follow the sequence: MgâMMT>AlâMMT>LiâMMT>NaâMMT>NH4âMMT>CsâMMT The decrease of the radon release rate (ÎE) determined by ETA that characterized microstructure changes due to collapse of interlayer space corresponded well to differences in the c-axis basal spacing (Îd 001) values determined from the XRD patterns before and after samples dehydration.Peer Reviewe
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