Stopping of slow recoil atoms in gases

Nuclear Resonance Fluorescence spectra contain information on the slowing-down behaviour of recoiling atoms in the energy range pertinent to the specific reaction. On the basis of conventional transport theory, measured spectra for arsenic atoms with energies ?15 eV slowing down in helium are analysed. The assumption of continuous slowing down turns out to be well justified, and the thermal motion of the gas atoms is shown to influence the effective stopping power only slightly. Somewhat surprising in view of uncertainties concerning the charge state of the recoiling atoms, theoretical predictions based on Lenz-Jensen elastic interaction agree well with the measured spectra. At present, the experimental data do not allow direct inversion, but the calculated spectra are shown to depend sensitively on the stopping-power input.     

Identification of the aromatase inhibitor letrozole in urine by gas chromatography/mass spectrometry

Letrozole (1-(bis-(4-cyanophenyl)methyl)-1,2,4-triazole) is used therapeutically as a non-steroidal aromatase inhibitor (Femara) to treat hormone-sensitive breast cancer in postmenopausal women. For doping purposes it may be used to counteract the adverse effects of an extensive abuse of anabolic androgenic steroids (gynaecomastia) and to increase the testosterone concentration by stimulation of the testosterone biosynthesis. The use of aromatase inhibitors has been prohibited by IOC/WADA regulations for male and female athletes since September 2001 and January 2005, respectively. Spot urine samples from women suffering from metastatic breast cancer and being treated with letrozole were collected and analysed to develop/optimise the detection system for metabolites of letrozole to allow the identification of athletes who do not comply with the internationally prohibited use of this cancer drug. The assay was based on gas chromatography/mass spectrometry (GC/MS) and the main metabolite of letrozole (bis-4-cyanophenylmethanol) was identified by comparison of its mass spectrum and retention time with that of a bis-4-cyanophenylmethanol reference. The full-scan spectrum, diagnostic ions and a validation of the method for the analysis of bis-4-cyanophenylmethanol are presented.     

Stopping of swift hydrogen diclusters: oscillator model

Enhanced stopping of swift hydrogen diclusters has been analysed theoretically. The target has been modeled as a gas of harmonic-oscillator atoms of variable density. This model predicts a proximity effect, i.e., enhanced stopping at high beam energy, and an oscillatory behavior at low energy. Both features get less pronounced with increasing target density due to increased screening of the ion-target interaction by polarization of the medium. Static screening by electrons accompanying the cluster likewise reduces the proximity effect. The Barkas-Andersen correction has been estimated in the Z₁³Z_1^3 limit. Our findings are in contrast with measurements on SiO₂ [S.M. Shubeita et al., Phys. Rev. B 77, 115327 (2008)] which showed a pronounced step in the energy dependence of the proximity effect.     

On the conundrum of deriving exact solutions from approximate master equations

We derive the exact time-evolution for a general quantum system under the influence of a bosonic bath that causes pure phase noise and demonstrate that for a Gaussian initial state of the bath, the exact result can be obtained also within a perturbative time-local master equation approach already in second order of the system–bath coupling strength. We reveal that this equivalence holds if the initial state of the bath can be mapped to a Gaussian phase-space distribution function. Moreover, we discuss the relation to the standard Bloch–Redfield approach.     

Analysis of octopamine in human doping control samples

The biogenic amine octopamine [4‐(2‐amino‐1‐hydroxyethyl)phenol] is prohibited in sports owing to its stimulating and performance‐enhancing properties. Adverse analytical findings in athletes' doping control samples commonly result from surreptitious applications; however, the occurrence of octopamine in nutritional supplements and in selected invertebrates as well as the assumption that its N‐methylated analog synephrine [4‐(1‐hydroxyethyl‐2‐methylamino)phenol, not banned by anti‐doping authorities but currently monitored in prevalence studies) might be converted in‐vivo into octopamine have necessitated a study to investigate the elimination of synephrine and octopamine present in over‐the‐counter products. Urine samples collected after administration of nutritional supplements containing octopamine and/or synephrine as well as urine samples collected after therapeutic application of octopamine‐ or synephrine‐containing drugs were analyzed using a validated solid‐phase extraction‐based procedure employing a weak cation exchange resin and liquid chromatographic/tandem mass spectrometric detection with electrospray ionization and multiple reaction monitoring. In the case of therapeutic octopamine application, the urinary concentration of the target compound increased from baseline levels below the lower limit of detection to 142 µg/mL, while urine samples collected after synephrine as well as dietary supplement administration did not yield any evidence for elevated renal excretion of octopamine. Copyright © 2011 John Wiley & Sons, Ltd.     

Topology optimization for nano‐photonics

Topology optimization is a computational tool that can be used for the systematic design of photonic crystals, waveguides, resonators, filters and plasmonics. The method was originally developed for mechanical design problems but has within the last six years been applied to a range of photonics applications. Topology optimization may be based on finite element and finite difference type modeling methods in both frequency and time domain. The basic idea is that the material density of each element or grid point is a design variable, hence the geometry is parameterized in a pixel‐like fashion. The optimization problem is efficiently solved using mathematical programming‐based optimization methods and analytical gradient calculations. The paper reviews the basic procedures behind topology optimization, a large number of applications ranging from photonic crystal design to surface plasmonic devices, and lists some of the future challenges in non‐linear applications.     

Determination of N-desmethyl- and N-bisdesmethyl metabolites of Sibutramine in doping control analysis using liquid chromatography-tandem mass spectrometry

Since January 2006, the list of prohibited substances established by the World Anti-Doping Agency includes the antidepressant / anti-obesity drug Sibutramine. Due to its rapid degradation to its active metabolites N-desmethyl and N-bisdesmethyl Sibutramine, reference compounds were synthesized and included into an existing screening assay to allow the unambiguous determination of these metabolic products in human urine using liquid-liquid extraction followed by liquid chromatography/tandem mass spectrometry. Characteristic product ions, obtained after electrospray ionization and collision-induced dissociation, were elucidated using high resolution/high accuracy mass measurements with a hybrid linear ion trap/orbitrap mass analyzer. Based on diagnostic product ions, the extended screening procedure was validated for both Sibutramine metabolites using a triple quadrupole mass spectrometer. Items such as lower limits of detection (6-40 ng mL(-1)), recoveries (39-42%), intraday precision (low: 5.5-10.6%, medium: 4.9-5.9%), high: 12.8-16.4%) and interday precision (low: 15.0-22.8%, medium: 17.7-18.6%), high: 16.5-25.6%) were evaluated, and a clinical spot urine sample was analyzed to demonstrate the applicability of the developed assay in sports drug testing.     

Screening for benfluorex and its major urinary metabolites in routine doping controls

Benfluorex [1-(m-trifluoromethylphenyl)-2-(β-benzoyloxyethyl)aminopropane] has been widely used for the treatment of atherogenic metabolic disorders and impaired carbohydrate metabolism (particularly in obese type-II diabetic patients) as well as an anorectic drug. Due to its potentially performance-enhancing properties, benfluorex has been added to the list of prohibited compounds and methods of doping by the World Anti-Doping Agency (WADA) in 2010, necessitating the implementation of the drug as well as its major metabolites into routine doping control procedures. In the present study, human urinary metabolites of benfluorex were characterized by gas chromatography–electron ionization–mass spectrometry (GC-EI-MS) as well as liquid chromatography–electrospray ionization–high resolution/high accuracy tandem mass spectrometry (LC-ESI-MS/MS). Commonly employed sports drug testing approaches consisting of liquid–liquid extraction followed by GC-MS or urine dilution and immediate LC-MS/MS analysis were expanded and validated with regard to specificity, recovery (48–54%, GC-MS only), intra- and interday precision (<25%), limits of detection (5–8 ng/mL for LC-MS/MS and 80 ng/mL for GC-MS), and ion suppression (for LC-ESI-MS/MS only) to allow the detection of benfluorex metabolites 1-(m-trifluoromethylphenyl)-2-(2-hydroxyethyl)aminopropane (M1), 1-(m-trifluoromethylphenyl)-2-(2-carboxymethyl)aminopropane (M2), and 1-(m-trifluoromethylphenyl)-2-aminopropane (M3) as well as the glucuronic acid conjugate of M1.     

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