493 research outputs found
Impact of glucuronide interferences on therapeutic drug monitoring of posaconazole by tandem mass spectrometry
Background: Posaconazole is a novel antifungal drug for oral application intended especially for therapy of invasive mycoses. Due to variable gastrointestinal absorption, adverse side effects, and suspected drug-drug interactions, therapeutic drug monitoring (TDM) of posaconazole is recommended. Method: A fast ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for quantification of posaconazole with a run-time <3 min was developed and compared to a LC-MS/MS method and HPLC method with fluorescence detection. Results: During evaluation of UPLC-MS/MS, two earlier eluting peaks were observed in the MRM trace of posaconazole. This was only seen in patient samples, but not in spiked calibrator samples. Comparison with LC-MS/MS disclosed a significant bias with higher concentrations measured by LC-MS/MS, while UPLC-MS/MS showed excellent agreement with the commercially available HPLC method. In the LC-MS/MS procedure, comparably wide and left side shifted peaks were noticed. This could be ascribed to in-source fragmentation of conjugate metabolites during electrospray ionisation. Precursor and product ion scans confirmed the assumption that the additional compounds are posaconazole glucuronides. Reducing the cone voltage led to disappearance of the glucuronide peaks. Slight modification of the LC-MS/MS method enabled separation of the main interference, leading to significantly reduced deviation. Conclusions: These results highlight the necessity to reliably eliminate interference from labile drug metabolites for correct TDM results, either by sufficient separation or selective MS conditions. The presented UPLC-MS/MS method provides a reliable and fast assay for TDM of posaconazole. Clin Chem Lab Med 2010; 48:1723-31
Numerical simulations of the Princeton magneto-rotational instability experiment with conducting axial boundaries
We investigate numerically the Princeton magneto-rotational instability (MRI)
experiment and the effect of conducting axial boundaries or endcaps. MRI is
identified and found to reach a much higher saturation than for insulating
endcaps. This is probably due to stronger driving of the base flow by the
magnetically rather than viscously coupled boundaries. Although the
computations are necessarily limited to lower Reynolds numbers () than
their experimental counterparts, it appears that the saturation level becomes
independent of when is sufficiently large, whereas it has been
found previously to decrease roughly as with insulating endcaps.
The much higher saturation levels will allow for the first positive detection
of MRI beyond its theoretical and numerical predictions
Nonlinear excitation of low-n harmonics in reduced magnetohydrodynamic simulations of edge-localized modes
Nonlinear simulations of the early ELM phase based on a typical type-I ELMy
ASDEX Upgrade discharge have been carried out using the reduced MHD code JOREK.
The analysis is focused on the evolution of the toroidal Fourier spectrum. It
is found that during the nonlinear evolution, linearly subdominant low-n
Fourier components, in particular the n = 1, grow to energies comparable with
linearly dominant harmonics. A simple model is developed, based on the idea
that energy is transferred among the toroidal harmonics via second order
nonlinear interaction. The simple model reproduces and explains very well the
early nonlinear evolution of the toroidal spectrum in the JOREK simulations.
Furthermore, it is shown for the n = 1 harmonic, that its spatial structure
changes significantly during the transition from linear to nonlinearly driven
growth. The rigidly growing structure of the linearly barely unstable n = 1
reaches far into the plasma core. In contrast, the nonlinearly driven n = 1 has
a rigidly growing structure localized at the plasma edge, where the dominant
toroidal harmonics driving the n = 1 are maximal and in phase. The presented
quadratic coupling model might explain the recent experimental observation of
strong low-n components in magnetic measurements [Wenninger et al., Non-linear
magnetic perturbations during edge localized modes in TCV dominated by low n
mode components, submitted to Nuclear Fusion]
Comments on "Volume ignition of mixed fuel" by H. Ruhl and G. Korn (Marvel Fusion, Munich)
In the most recent note on Marvel Fusion's concept for a laser driven pB
reactor without compression, Ruhl and Korn consider the volumetric energy
balance of fusion reactions vs. bremsstrahlung losses in a mixed fuel (DT and
pB) environment and claim the satisfaction of this necessary "ideal ignition"
condition. Their results are based, however, on improper assumptions about the
deposition of fusion energy in the plasma. Correcting for them, we show that
the quoted composition of their fuel (a solid boron composite, binding high
concentrations of D, T and p) would actually preclude ignition due to the high
bremsstrahlung losses associated with the presence of boron. To facilitate
ignition, Ruhl and Korn also consider the reduction of the bremsstrahlung
losses by confining the radiation in the optically thin fuel region by high Z
walls. They suggest to preload this region with radiation so that the radiation
temperature equals approximately that of the plasma constituents . We show that in this set-up the radiation energy -
neglected in these considerations - would, however, vastly exceed the thermal
energy of the plasma and actually dominate the ignition energy requirements.Comment: 6 pages, 1 figur
Testing of the new JOREK stellarator-capable model in the tokamak limit
In preparation for extending the JOREK nonlinear MHD code to stellarators, a
hierarchy of stellarator-capable reduced and full MHD models has been derived
and tested. The derivation was presented at the EFTC 2019 conference.
Continuing this line of work, we have implemented the reduced MHD model
(arXiv:1907.12486) as well as an alternative model which was newly derived
using a different set of projection operators for obtaining the scalar momentum
equations from the full MHD vector momentum equation. With the new operators,
the reduced model matches the standard JOREK reduced models for tokamaks in the
tokamak limit and conserves energy exactly, while momentum conservation is less
accurate than in the original model whenever field-aligned flow is present.Comment: 23 pages, 1 table, 7 figures. Submitted to Journal of Plasma Physic
A three-dimensional reduced MHD model consistent with full MHD
Within the context of a viscoresistive magnetohydrodynamic (MHD) model with
anisotropic heat transport and cross-field mass diffusion, we introduce novel
three-term representations for the magnetic field (background vacuum field,
field line bending and field compression) and velocity (
flow, field-aligned flow and fluid compression), which are amenable to
three-dimensional treatment. Once the representations are inserted into the MHD
equations, appropriate projection operators are applied to Faraday's law and
the Navier-Stokes equation to obtain a system of scalar equations that is
closed by the continuity and energy equations. If the background vacuum field
is sufficiently strong and the is low, MHD waves are approximately
separated by the three terms in the velocity representation, with each term
containing a specific wave. Thus, by setting the appropriate term to zero, we
eliminate fast magnetosonic waves, obtaining a reduced MHD model. We also show
that the other two velocity terms do not compress the magnetic field, which
allows us to set the field compression term to zero within the same reduced
model. Dropping also the field-aligned flow, a further simplified model is
obtained, leading to a fully consistent hierarchy of reduced and full MHD
models for 3D plasma configurations. Finally, we discuss the conservation
properties and derive the conditions under which the reduction approximation is
valid. We also show that by using an ordering approach, reduced MHD equations
similar to what we got from the ansatz approach can be obtained by means of a
physics-based asymptotic expansion.Comment: 18 pages. This article was published in Physics of Plasma
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