Temperature-programmed gas chromatography linear retention indices of all C4-C30 monomethylalkanes on methylsilicone OV-1 stationary phase. Contribution towards a better understanding of volatile organic compounds in exhaled breath

Monomethylated alkanes have been proposed to be contained in exhaled breath, their concentration pattern serving for identification of lung carcinoma, breast carcinoma and rejection of foreign tissue after heart transplant rejection. Improving the accuracy of identification for monomethylated alkanes will enhance work on their biochemical background which presently is unknown. The programmed temperature linear retention indices of all 196 C(4)-C(30) monomethylalkanes on OV-1 stationary phase were measured with an average repeatability of +/-0.07 index units (i.u.). The mixture of C(9)-C(30) monomethylalkanes was prepared by methylene insertion reaction to C(8)-C(29)n-alkanes mixture. The preliminary identification of monomethylalkanes was performed on the basis of the dependence of homomorphy factors on the number of carbon atoms of individual homologous series of monomethylalkanes (retention indices extrapolated with s=0.15 i.u.). The prediction of retention of isomers with new position of methyl group beginning at higher carbon atoms number, as well as for second, third, fourth, etc., member of homologous series allowed the dependence H(P)=f(C(n)) for first, second, third, etc., members of beginning homologous of monomethylalkane series (retention indices extrapolated with s=0.17 i.u.). The identification was confirmed by mass spectrometry. All gas chromatographic unseparated monomethylalkane isomers with methyl-group near the middle of molecule carbon chain were resoluted by mass spectrometric deconvolution. Obtained regular dependences H(P)=f(C(n)) allow precise retention prediction of monomethylalkanes C(30).     

Synchronization is enhanced in weighted complex networks

The propensity for synchronization of complex networks with directed and weighted links is considered. We show that a weighting procedure based upon the global structure of network pathways enhances complete synchronization of identical dynamical units in scale-free networks. Furthermore, we numerically show that very similar conditions hold also for phase synchronization of nonidentical chaotic oscillators.     

Femtosecond formation of coupled phonon-plasmon modes in InP: Ultrabroadband THz experiment and quantum kinetic theory

The ultrafast transition of an optical phonon resonance to a coupled phonon-plasmon system is studied. After 10-fs photoexcitation of i-InP, the buildup of coherent beats of the emerging hybrid modes is directly monitored via ultrabroadband THz spectroscopy. The anticrossing is mapped out as a function of time and density. A quantum kinetic theory of microscopic carrier-carrier and carrier-LO-phonon interactions explains the delayed formation of the collective modes. The buildup time is quantitatively reproduced to scale with the oscillation cycle of the upper branch of the coupled resonance.     

Ein Existenz- und Eindeutigkeitssatz für die Hammersteinsche Gleichung in Banachräumen

Ohne Zusammenfassung     

A serial functional connectivity MRI study in healthy individuals assessing the variability of connectivity measures: reduced interhemispheric connectivity in the motor network during continuous performance

To date, little data is available on the reproducibility of functional connectivity MRI (fcMRI) studies. Here, we tested the variability and reproducibility of both the functional connectivity itself and different statistical methods to analyze this phenomenon. In the main part of our study, we repeatedly examined two healthy subjects in 10 sessions over 6 months with fcMRI. Cortical areas involved in motor function were examined under two different cognitive states: during continuous performance (CP) of a flexion/extension task of the fingers of the right hand and while subjects were at rest. Connectivity to left primary motor cortex (lSM1) was calculated by correlation analysis. The resulting correlation coefficients were transformed to z-scores of the standard normal distribution. For each subject, multisession statistical analyses were carried out with the z-score maps of the resting state (RS) and the CP experiments. First, voxel based t tests between the two groups of fcMRI experiments were performed. Second, ROI analyses were carried out for contralateral right SM1 and for supplementary motor area (SMA). For both ROI, mean and maximum z-score were calculated for each experiment. Also, the fraction of significantly (P<.05) correlated voxels (FCV) in each ROI was calculated. To evaluate the differences between the RS and the CP condition, paired t tests were performed for the mean and maximum z-scores, and Wilcoxon signed ranks tests for matched pairs were carried out for the FCV. All statistical methods and connectivity measures under investigation yielded a distinct loss in left–right SM1 connectivity under the CP condition. For SMA, interindividual differences were apparent. We therefore repeated the fcMRI experiments and the ROI analyses in a group of seven healthy subjects (including the two subjects of the main study). In this substudy, we were able to verify the reduction of left–right SM1 connectivity during unilateral performance. Still, the direction of SMA to lSM1 connectivity change during the CP condition remained undefined as four subjects showed a connectivity increase and three showed a decrease. In summary, we were able to demonstrate a distinct reduction in left–right SM1 synchrony in the CP condition compared to the RS both in the longitudinal and in the multisubject study. This effect was reproducible with all statistical methods and all measures of connectivity under investigation. We conclude that despite intra- and interindividual variability, serial and cross-sectional assessment of functional connectivity reveals stable and reliable results.     

Ultramikroskopie der Jodlösungen II

Ohne Zusammenfassung     

Stereospecific Syntheses of 7β-AND 7α -Hydroxycholesterols

The stereospecific syntheses of 7β-AND 7α‐hydroxycholesterols from cholesterol are described.     

Ultramikroskopische Beobachtungen

Ohne Zusammenfassung     

Permeation profiles of potential urine-borne biomarkers of human presence over brick and concrete

Headspace solid phase micro-extraction gas chromatography-mass spectrometry (SPME-GC-MS) analysis was performed over an in-house made filling chamber loaded with brick or concrete, mimicking a potential entrapment scene of building collapse following natural or man-made disasters. Permeation profiles of 22 volatile species, released by human urine samples, were quantitatively monitored over the selected debris materials for a time period of 24 hours (LODs ranged from 0.05-0.8 ppb, R(2) varied from 0.991-0.999 and RSDs 3-9%). Ketones were the most abundant constituents of urine vapor with eleven representatives followed by five aldehydes, two furans, two sulphur-containing compounds, one nitrile and one heterocyclic compound. The majority of the detected compounds were found below 10 ppb, with the exception of some ketones including acetone, 2-butanone and 2-pentanone. The influence of debris materials on the permeation profiles of analytes under study depended on their fundamental physicochemical properties. Less volatile and more soluble compounds in urine (ketones and aldehydes) were found to be present for longer time periods in the surroundings of the urine samples than the more volatile and poorly soluble ones (furans, sulphur-containing compounds). More specifically, ketones exhibited longer residence times in the filling chamber and strongly interacted with the debris materials as their molecular masses were increased; their profiles were found to be significantly modified in the presence of concrete. In general, concrete demonstrated a stronger interaction with urine species than brick, affecting the observed concentrations and residence times of released volatiles in the chamber.     

Breath acetone monitoring by portable Si:WO3 gas sensors

Breath analysis has the potential for early stage detection and monitoring of illnesses to drastically reduce the corresponding medical diagnostic costs and improve the quality of life of patients suffering from chronic illnesses. In particular, the detection of acetone in the human breath is promising for non-invasive diagnosis and painless monitoring of diabetes (no finger pricking). Here, a portable acetone sensor consisting of flame-deposited and in situ annealed, Si-doped epsilon-WO₃ nanostructured films was developed. The chamber volume was miniaturized while reaction-limited and transport-limited gas flow rates were identified and sensing temperatures were optimized resulting in a low detection limit of acetone (∼20 ppb) with short response (10–15 s) and recovery times (35–70 s). Furthermore, the sensor signal (response) was robust against variations of the exhaled breath flow rate facilitating application of these sensors at realistic relative humidities (80–90%) as in the human breath. The acetone content in the breath of test persons was monitored continuously and compared to that of state-of-the-art proton transfer reaction mass spectrometry (PTR-MS). Such portable devices can accurately track breath acetone concentration to become an alternative to more elaborate breath analysis techniques.