Interior of nonuniform black strings

We consider nonuniform black strings inside their event horizon. We present numerical evidence, that the singularity touches the horizon as the horizon topology changing transition is reached.     

Different responses of E:Z‐isomers of pesticides in liquid chromatography–electrospray ionization–mass spectrometry

The mass spectrometric behavior of four pairs of stereoisomers was investigated by liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS). The E‐ and Z‐isomers of the pesticides chlorfenvinphos, dimethomorph, mevinphos and phosphamidon—each with one double bond—were chosen for this study. The MS response of the individual isomers was investigated by infusing the isomers individually into the MS or after the separation of isomer mixtures via high‐performance liquid chromatography(HPLC). In the case of dimethomorph, the same MS response was found for the two isomers. In contrast to that, the individual isomers of chlorfenvinphos, mevinphos and phosphamidon showed different MS response both in the single ion monitoring (SIM) mode in single quadrupole MS and multiple reaction monitoring (MRM) mode in tandem MS. The MS response of the isomers partly depends on (1) the declustering potential of the precursor ion in the SIM mode, (2) the selected transition and (3) the collision energy in the MRM mode. Consequently, quantification by summation of the peak areas of the isomers is inaccurate due to over‐ or underestimating of one of the stereoisomers. Accurate quantitative results can only be achieved when the compound‐specific MS parameters are separately determined for each isomer. This can be done by using pure isomers or by the determination of the MS parameters after HPLC separation and the measurement of the actual isomer ratio with an independent technique. Copyright © 2010 John Wiley & Sons, Ltd.     

A liquid chromatography–atmospheric pressure photoionization tandem mass spectrometric method for the determination of azaarenes in atmospheric particulate matter

The development, optimization and validation of a liquid chromatography–atmospheric pressure photoionization tandem mass spectrometric (LC–APPI/MS/MS) method for the determination of 15 azaarenes (4-azafluorene, benzo[h] and -[f]quinoline, phenanthridine, acridine, 1-azafluoranthene, 4-azapyrene, benz[a]- and -[c]acridine, -10-azabenzo[a]pyrene, 7,9- and 7,10-dimethylbenz[c]acridine, dibenz[a,j]-, -[c,h] and [a,i]acridine) in airborne particulate matter is described. Each compound was detected and quantified operating in multiple reaction monitoring mode. Extraction of azaarenes was achieved using accelerated solvent extraction (ASE) with dichlormethane/methanol (50/50, v/v). After extraction, no additional clean-up procedure like solid phase or liquid/liquid extraction was necessary. Limits of quantification (S/N × 10) ranged from 0.2 pg/μl to 1.4 pg/μl, matrix dependent recoveries were between 57% and 94%, with relative standard deviations from 8% to 17%. Applicability of the method was demonstrated analyzing 10 samples of particulate matter (PM_2.5) collected in winter 2008. In all samples dimethylbenz[c]acridines as well as dibenzacridines were below the limit of quantification, concentration of the remaining analytes were in the range from 0.002 ng/m³ to 0.356 ng/m³.     

Rotating black holes in dilatonic Einstein-Gauss-Bonnet theory

We construct generalizations of the Kerr black holes by including higher-curvature corrections in the form of the Gauss-Bonnet density coupled to the dilaton. We show that the domain of existence of these Einstein-Gauss-Bonnet-dilaton (EGBD) black holes is bounded by the Kerr black holes, the critical EGBD black holes, and the singular extremal EGBD solutions. The angular momentum of the EGBD black holes can exceed the Kerr bound. The EGBD black holes satisfy a generalized Smarr relation. We also compare their innermost stable circular orbits with those of the Kerr black holes and show the existence of differences which might be observable in astrophysical systems.     

A convergent and precise finite element scheme for Landau–Lifschitz–Gilbert equation

In this paper, we propose a new scheme for the numerical integration of the Landau–Lifschitz–Gilbert (LLG) equations in their full complexity, in particular including stray-field interactions. The scheme is consistent up to order 2 (in time), and unconditionally stable. It combines a linear inner iteration with a non-linear renormalization stage for which a rigorous proof of convergence of the numerical solution toward a weak solution is given, when both space and time stepsizes tend to \(0\) . A numerical implementation of the scheme shows its performance on physically relevant test cases. We point out that to the knowledge of the authors this is the first finite element scheme for the LLG equations which enjoys such theoretical and practical properties.     

Simultaneous determination of Hg(II) and alkylated Hg, Pb, and Sn species in human body fluids using SPME-GC/MS-MS

A GC/MS-MS method for the determination of Hg(II) and alkylated Hg, Pb, and Sn species in human urine is described. Separation and identification of the metal species are performed by capillary gas chromatography coupled with an ion-trap mass spectrometer with electron impact ionization in the tandem-MS mode. For sample preparation a very promising technique was applied that is based on a derivatization with sodium tetraethylborate followed by headspace solid phase microextraction (SPME). Operation of the used ion trap in the tandem-MS mode yields in improved detection limits because of a signal-to-noise ratio that is at least one order of magnitude better than in the MS mode. The detection limits in real matrices like urine are between 7 and 22 ng/L for all species investigated. Urinary levels of inorganic Hg in non-occupationally exposed persons with and without dental amalgam were found to be between 0.1 and 1.4 μg/L. A reference material (“ClinRep, Level I”) was used for quality assurance. Compared to the coupling of GC with ICP-MS (“inorganic” MS), the advantage of the proposed method using an “organic” MS is that (i) the species can be directly identified via their precursor and daughter ions and (ii) analysis can be performed with a commercially available hyphenated technique at moderate costs and needs no lab-made interfacing. Moreover, it offers a real multi-element/multi-species capability with low detection limits and a minimum of sample preparation.     

Dynamics of gold clusters on amorphous carbon films induced by annealing in a transmission electron microscope

The change of the size distribution of Au clusters induced by annealing was studied in situ by transmission electron microscopy. Starting from statistically distributed Au clusters on a thin amorphous carbon film, “islands” are formed within a few months storage at room temperature, which consist of Au clusters with sizes <4 nm embedded in a thin Au film. These islands cover originally areas with sizes around 25 × 70 nm². If the temperature is increased in the transmission electron microscope two different processes can be clearly distinguished that lead to the coarsening of the cluster size distribution: cluster coalescence and (contactless) Ostwald ripening. The degree and rate of the coarsening are found to depend on the underlying surface (Au film or amorphous carbon) and the exposure to the high-flux high-energy electron beam, which can be estimated to lead to high-temperature excursions in a cluster on a 10⁻¹² s time scale. The experimental findings are confirmed by Monte-Carlo simulations using the many-body Gupta potentials in order to calculate the Au/Au interaction. Moreover, the results of MC simulations suggest an electron-beam induced formation of a “quasi-two-dimensional gas” of small highly mobile Au species on the Au film, which promotes Ostwald ripening.     

Development and validation of a rapid LC-ESI-MS/MS method for quantification of fluoxetine and its application to MS binding assays

In the present study, a rapid and sensitive LC-ESI-MS/MS method for quantification of (S)-fluoxetine as a native marker in mass spectrometry (MS) binding assays addressing the human serotonin transporter (hSERT) was developed and validated. The concept of MS binding assays based on mass spectrometric quantification of a nonlabeled marker recently introduced by us represents a promising alternative to conventional radioligand binding without the drawbacks inherently connected with radioisotope labeling. For high-performance liquid chromatography (HPLC), a 20 × 2-mm RP-18 column with a mobile phase composed of acetonitrile and ammonium bicarbonate buffer (5 mmol L⁻¹, pH 9.5) at a ratio of 80:20 (v/v) and a flow rate of 800 μL min⁻¹ in an isocratic mode were used, resulting in a chromatographic cycle time of 60 s. Employing [²H₅]fluoxetine as internal standard enabled ESI-MS/MS quantification of (S)-fluoxetine between 3 nmol L⁻¹ and 50 pmol L⁻¹ (LLOQ) in matrix obtained from binding experiments without the need of any sample preparation. Validation of the method showed that linearity, intra-, and inter-batch accuracy as well as precision meet the requirements of the FDA guidance for bioanalytical method validation. Considering sensitivity and speed, the established method is clearly superior to those published for biological matrices so far. Furthermore, the method was transferred to other RP-18 columns of different lengths and respective validation experiments demonstrated its versatility and chromatographic robustness. Finally, the newly developed method was successfully applied to MS binding assays for hSERT. The affinity determined for (S)-fluoxetine in saturation experiments was in good agreement with literature data obtained in respective radioligand binding assays.     

A theoretical description of elastic pillar substrates in biophysical experiments.

Arrays of elastic pillars are used in biophysical experiments as sensors for traction forces. The evaluation of the forces can be complicated if they are coupled to the pillar displacements over large distances. This is the case if many of the pillars are interconnected by elastic linkages as, for example, in fiber networks that are grown on top of pillars. To calculate the traction forces in such a network, we developed a set of nonlinear inhomogeneous equations relating the forces in the linking elements to the resulting pillar deflections. We chose a homogeneous, activated two-dimensional network of cytoskeletal actin filaments to illustrate that a pillar substrate is generally not a force sensor but a force-gradient sensor. In homogeneous networks the forces acting along the filaments can be approximated by analyzing only pillar deflections in the edge zones of the substrate and by integration over the corresponding force gradients.