1,292 research outputs found
Pharmacokinetic models for propofol-defining and illuminating the devil in the detail
The recently introduced open-target-controlled infusion (TCI) systems can be programmed with any pharmacokinetic model, and allow either plasma- or effect-site targeting. With effect-site targeting the goal is to achieve a user-defined target effect-site concentration as rapidly as possible, by manipulating the plasma concentration around the target. Currently systems are pre-programmed with the Marsh and Schnider pharmacokinetic models for propofol. The former is an adapted version of the Gepts model, in which the rate constants are fixed, whereas compartment volumes and clearances are weight proportional. The Schnider model was developed during combined pharmacokinetic-pharmacodynamic modelling studies. It has fixed values for V1, V3, k(13), and k(31), adjusts V2, k(12), and k(21) for age, and adjusts k(10) according to total weight, lean body mass (LBM), and height. In plasma targeting mode, the small, fixed V1 results in very small initial doses on starting the system or on increasing the target concentration in comparison with the Marsh model. The Schnider model should thus always be used in effect-site targeting mode, in which larger initial doses are administered, albeit still smaller than for the Marsh model. Users of the Schnider model should be aware that in the morbidly obese the LBM equation can generate paradoxical values resulting in excessive increases in maintenance infusion rates. Finally, the two currently available open TCI systems implement different methods of effect-site targeting for the Schnider model, and in a small subset of patients the induction doses generated by the two methods can differ significantly
Classification of Higher Dimensional Spacetimes
We algebraically classify some higher dimensional spacetimes, including a
number of vacuum solutions of the Einstein field equations which can represent
higher dimensional black holes. We discuss some consequences of this work.Comment: 16 pages, 1 Tabl
De consumptie van dierlijke producten : ontwikkelingen, invloedsfactoren, actoren en interventies
LEI Wageningen UR heeft in opdracht van het Planbureau voor de Leefomgeving (PBL) met behulp van kwantitatief onderzoek onderzocht hoe de consumptie van dierlijke producten zich in Europese landen in de afgelopen decennia heeft ontwikkeld. Daarnaast zijn met behulp van kwalitatief onderzoek mogelijke interventies geïdentificeerd gericht op het beïnvloeden van de consumptie van dierlijke producten. Dit onderzoek biedt een basis voor de verdere uitwerking en uitvoering van door publieke en private actoren te nemen maatregelen gericht op verandering of vermindering van de consumptie van dierlijke producten
Spinor classification of the Weyl tensor in five dimensions
We investigate the spinor classification of the Weyl tensor in five
dimensions due to De Smet. We show that a previously overlooked reality
condition reduces the number of possible types in the classification. We
classify all vacuum solutions belonging to the most special algebraic type. The
connection between this spinor and the tensor classification due to Coley,
Milson, Pravda and Pravdov\'a is investigated and the relation between most of
the types in each of the classifications is given. We show that the black ring
is algebraically general in the spinor classification.Comment: 40 page
Layer charge instability in unbalanced bilayer systems in the quantum Hall regime
Measurements in GaAs hole bilayers with unequal layer densities reveal a
pronounced magneto-resistance hysteresis at the magnetic field positions where
either the majority or minority layer is at Landau level filling factor one. At
a fixed field in the hysteretic regions, the resistance exhibits an unusual
time dependence, consisting of random, bidirectional jumps followed by slow
relaxations. These anomalies are apparently caused by instabilities in the
charge distribution of the two layers.Comment: 4 pages, 4 figure
O3/O7 Orientifold Truncations and Very Special Quaternionic-Kaehler Geometry
We study the orientifold truncation that arises when compactifying type II
string theory on Calabi-Yau orientifolds with O3/O7-planes, in the context of
supergravity. We look at the N=2 to N=1 reduction of the hypermultiplet sector
of N=2 supergravity under the truncation, for the case of very special
quaternionic-Kaehler target space geometry. We explicitly verify the Kaehler
structure of the truncated spaces, and we study the truncated isometry algebra.
For symmetric special quaternionic spaces, we give a complete overview of the
spaces one finds after truncation. We also find new examples of dual Kaehler
spaces, that give rise to flat potentials in N=1 supergravity.Comment: 25 pages, LaTeX, v2:curvature tensor of the dual symmetric spaces
calculated, section 7 expanded, references added, v3:few typos fixed, version
to appear in Class.Quantum Gravit
Perfectly Translating Lattices on a Cylinder
We perform molecular dynamics simulations on an interacting electron gas
confined to a cylindrical surface and subject to a radial magnetic field and
the field of the positive background. In order to study the system at lowest
energy states that still carry a current, initial configurations are obtained
by a special quenching procedure. We observe the formation of a steady state in
which the entire electron-lattice cycles with a common uniform velocity.
Certain runs show an intermediate instability leading to lattice
rearrangements. A Hall resistance can be defined and depends linearly on the
magnetic field with an anomalous coefficient reflecting the manybody
contributions peculiar to two dimensions.Comment: 13 pages, 5 figure
Optimization of the gas flow in a GEM chamber and development of the GEM foil stretcher
The gas electron multiplier technology has been proven to tolerate rat e
larger than 50 MHz/cm2 without noticeable aging and to provide sub resolution
on working chambers up to 45 cm x 45 cm. A new gas electron multiplier-based
tracker is under development for the Hall A upgrade at Jefferson Lab. The
chambers of the tracker have been designed in a modular way: each chamber
consists of 3 adjacent gas electron multiplier modules, with an active area
of 40 cm x 50 cm each. We optimized the gas flow inside the gas electron
multiplier module volume, using the COMSOL physics simulator framework; the
COMSOL-based analysis includes the design of the inlet and outlet pipes and
the maximization of the uniformity of the gas flow. We have defined the
procedures for the assembling of the gas electron multiplier modules and
designed a mechanical system (TENDIGEM) that will be used to stretch the GEM
foils at the proper tension (few kg/cm); the TENDIGEM is based on the
original design developed at LNF
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