10,284 research outputs found
Fiberoptisch unterstützte endotracheale Intubation durch die Larynxmaske im Kindesalter
Zusammenfassung: Die fiberoptisch assistierte endotracheale Intubation durch die Larynxmaske ist ein sicheres Verfahren, um beim pädiatrischen Patienten mit unerwarteter sowie auch bei bekannter schwieriger Intubation den Atemweg einfach und zuverlässig zu sichern. Die Methode stellt eine Standardtechnik in der Atemwegssicherung dar; sie muss einerseits Bestandteil der klinischen Ausbildung sein und andererseits regelmäßig trainiert werden. Das Entfernen der Larynxmaske über den Endotrachealtubus wird durch dessen kurze Länge erschwert bzw. der Endotrachealtubus kann dabei sehr leicht aus der Trachea dislozieren. Nebst einer Vielzahl von Techniken, die Larynxmaske sicher über den Endotrachealtubus zu entfernen, bietet der Cook Airway Exchange Catheter in der Kinderanästhesie eine einfache Methode, nicht nur die Larynxmaske sicher über den Tubus zu entfernen, sondern anschließend auch den geeigneten Tubus einzuführen. Dies ist insbesondere bei gecufften Tuben wünschenswert, bei denen der Pilotballon des gecufften Tubus zu groß ist, um Larynxmasken der Größen 2,5 und kleiner zu passieren. Die vorliegende Arbeit zeigt schrittweise die fiberoptisch assistierte endotracheale Intubation durch die Larynxmaske beim Kind und diskutiert ihre Bedeutung. Eine Liste mit aufeinanderabgestimmten Größen von Larynxmasken, Endotrachealtuben und Airway Exchange Cathetern ist ebenfalls enthalte
Density-functional calculation of ionization energies of current-carrying atomic states
Current-density-functional theory is used to calculate ionization energies of
current-carrying atomic states. A perturbative approximation to full
current-density-functional theory is implemented for the first time, and found
to be numerically feasible. Different parametrizations for the
current-dependence of the density functional are critically compared. Orbital
currents in open-shell atoms turn out to produce a small shift in the
ionization energies. We find that modern density functionals have reached an
accuracy at which small current-related terms appearing in open-shell
configurations are not negligible anymore compared to the remaining difference
to experiment.Comment: 7 pages, 2 tables, accepted by Phys. Rev.
Behavioral and Electrophysiological Effects of Transcranial Direct Current Stimulation of the Parietal Cortex in a Visuo-Spatial Working Memory Task
Impairments of working memory (WM) performance are frequent concomitant symptoms in several psychiatric and neurologic diseases. Despite the great advance in treating the reduced WM abilities in patients suffering from, e.g., Parkinson’s and Alzheimer’s disease by means of transcranial direct current stimulation (tDCS), the exact neurophysiological underpinning subserving these therapeutic tDCS-effects are still unknown. In the present study we investigated the impact of tDCS on performance in a visuo-spatial WM task and its underlying neural activity. In three experimental sessions, participants performed a delayed matching-to-sample WM task after sham, anodal, and cathodal tDCS over the right parietal cortex. The results showed that tDCS modulated WM performance and its underlying electrophysiological brain activity in a polarity-specific way. Parietal tDCS altered event-related potentials and oscillatory power in the alpha band at posterior electrode sites. The present study demonstrates that posterior tDCS can alter visuo-spatial WM performance by modulating the underlying neural activity. This result can be considered an important step toward a better understanding of the mechanisms involved in tDCS-induced modulations of cognitive processing. This is of particular importance for the application of electrical brain stimulation as a therapeutic treatment of neuropsychiatric deficits in clinical populations
Probing the 5f Electrons in Am-I by Hybrid Density Functional Theory
The ground states of the actinides and their compounds continue to be matters
of considerable controversies. Experimentally, Americium-I (Am-I) is a
non-magnetic dhcp metal whereas theoretically an anti-ferromagnetic ground
state is predicted. We show that hybrid density functional theory, which
admixes a fraction of exact Hartree-Fock (HF) exchange with approximate DFT
exchange, can correctly reproduce the ground state properties of Am. In
particular, for a 0.40 fraction of HF exchange we obtain a non-magnetic ground
state with equilibrium atomic volume, bulk modulus, 5f electron population, and
the density of electronic states all in good agreement with experimental data.
We argue that the exact HF exchange corrects the overestimation of the
approximate DFT exchange interaction.Comment: 1 table, 4 figures. Chemical Physics Letters, in press (2009
Theoretical analysis of magnetic coupling in sandwich clusters V_n(C_6H_6)_{n+1}
The mechanism of ferromagnetism stability in sandwich clusters
V(CH) has been studied by first-principles calculation and
model analysis. It is found that each of the three types of bonds between V and
benzene (Bz) plays different roles. V 3d orbital, extending along the
molecular axis, is weakly hybridized with Bz's HOMO-1 orbital to form the
-bond. It is quite localized and singly occupied, which contributes
1 to the magnetic moment but little to the magnetic coupling of
neighboring V magnetic moments. The in-plane d, d orbitals
are hybridized with the LUMO of Bz and constitute the -bond. This
hybridization is medium and crucial to the magnetic coupling though the
states have no net contribution to the total magnetic moment.
d, d and HOMO of Bz form a quite strong -bond to hold the
molecular structure but they are inactive in magnetism because their energy
levels are far away from the Fermi level. Based on the results of
first-principles calculation, we point out that the ferromagnetism stability is
closely related with the mechanism proposed by Kanamori and Terakura [J.
Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the
presence of edge Bz's in the cluster introduces an important modification. A
simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure
On "the complete basis set limit" and plane-wave methods in first-principles simulations of water
Water structure, measured by the height of the first peak in oxygen-oxygen
radial distributions, is converged with respect to plane-wave basis energy
cutoffs for ab initio molecular dynamics simulations, confirming the
reliability of plane-wave methods.Comment: 9 pages, 3 figure
Electronic structure of crystalline binary and ternary Cd-Te-O compounds
The electronic structure of crystalline CdTe, CdO, -TeO,
CdTeO and CdTeO is studied by means of first principles
calculations. The band structure, total and partial density of states, and
charge densities are presented. For -TeO and CdTeO, Density
Functional Theory within the Local Density Approximation (LDA) correctly
describes the insulating character of these compounds. In the first four
compounds, LDA underestimates the optical bandgap by roughly 1 eV. Based on
this trend, we predict an optical bandgap of 1.7 eV for CdTeO. This
material shows an isolated conduction band with a low effective mass, thus
explaining its semiconducting character observed recently. In all these oxides,
the top valence bands are formed mainly from the O 2p electrons. On the other
hand, the binding energy of the Cd 4d band, relative to the valence band
maximum, in the ternary compounds is smaller than in CdTe and CdO.Comment: 13 pages, 15 figures, 2 tables. Accepted in Phys Rev
Spin Resolution of the Electron-Gas Correlation Energy: Positive same-spin contribution
The negative correlation energy per particle of a uniform electron gas of
density parameter and spin polarization is well known, but its
spin resolution into up-down, up-up, and down-down contributions is not.
Widely-used estimates are incorrect, and hamper the development of reliable
density functionals and pair distribution functions. For the spin resolution,
we present interpolations between high- and low-density limits that agree with
available Quantum Monte Carlo data. In the low-density limit for ,
we find that the same-spin correlation energy is unexpectedly positive, and we
explain why. We also estimate the up and down contributions to the kinetic
energy of correlation.Comment: new version, to appear in PRB Rapid Communicatio
Timesaving Double-Grid Method for Real-Space Electronic-Structure Calculations
We present a simple and efficient technique in ab initio electronic-structure
calculation utilizing real-space double-grid with a high density of grid points
in the vicinity of nuclei. This technique promises to greatly reduce the
overhead for performing the integrals that involves non-local parts of
pseudopotentials, with keeping a high degree of accuracy. Our procedure gives
rise to no Pulay forces, unlike other real-space methods using adaptive
coordinates. Moreover, we demonstrate the potential power of the method by
calculating several properties of atoms and molecules.Comment: 4 pages, 5 figure
Quantum mechanical ab-initio simulation of the electron screening effect in metal deuteride crystals
In antecedent experiments the electron screening energies of the d+d
reactions in metallic environments have been determined to be enhanced by an
order of magnitude in comparison to the case of gaseous deuterium targets. The
analytical models describing averaged material properties have not been able to
explain the experimental results so far. Therefore, a first effort has been
undertaken to simulate the dynamics of reacting deuterons in a metallic lattice
by means of an ab-initio Hartree-Fock calculation of the total electrostatic
force between the lattice and the successively approaching deuterons via path
integration. The calculations have been performed for Li and Ta, clearly
showing a migration of electrons from host metallic to the deuterium atoms.
However, in order to avoid more of the necessary simplifications in the model
the utilization of a massive parallel supercomputer would be required.Comment: 11 pages, 12 figures, svjour class. To be published in Eur. Phys. J.
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