High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): δ18O correlation between a Gerzensee-stack and NGRIP

Oxygen-isotope variations were analyzed on bulk samples of shallow-water lake marl from Gerzensee, Switzerland, in order to evaluate major and minor climatic oscillations during the late-glacial. To highlight the overall signature of the Gerzensee δ18O record, δ18O records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances. Then the records were stacked with a weighting depending on the differing sampling resolution. To develop a precise chronology, the δ18O-stack was then correlated with the NGRIP δ18O record applying a Monte Carlo simulation, relying on the assumption that the shifts in δ18O were climate-driven and synchronous in both archives. The established chronology on the GICC05 time scale is the basis for (1) comparing the δ18O changes recorded in Gerzensee with observed climatic and environmental fluctuations over the whole North Atlantic region, and (2) comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the Bølling/Allerød period. The δ18O record of Gerzensee is characterized by two major isotope shifts at the onset and at the termination of the Bølling/Allerød warm period, as well as four intervening negative shifts labeled GI-1e2, d, c2, and b, which show a shift of one third to one fourth of the major δ18O shifts at the beginning and end of the Bølling/Allerød. Despite some inconsistency in terminology, these oscillations can be observed in various climatic proxies over wide regions in the North Atlantic region, especially in reconstructed colder temperatures, and they seem to be caused by hemispheric climatic variations.

Three-dimensional magnetic resonance observation of cartilage repair tissue (MOCART) score assessed with an isotropic three-dimensional true fast imaging with steady-state precession sequence at 3.0 Tesla

INTRODUCTION: Cartilage defects are common pathologies and surgical cartilage repair shows promising results. In its postoperative evaluation, the magnetic resonance observation of cartilage repair tissue (MOCART) score, using different variables to describe the constitution of the cartilage repair tissue and the surrounding structures, is widely used. High-field magnetic resonance imaging (MRI) and 3-dimensional (3D) isotropic sequences may combine ideal preconditions to enhance the diagnostic performance of cartilage imaging.Aim of this study was to introduce an improved 3D MOCART score using the possibilities of an isotropic 3D true fast imaging with steady-state precession (True-FISP) sequence in the postoperative evaluation of patients after matrix-associated autologous chondrocyte transplantation (MACT) as well as to compare the results to the conventional 2D MOCART score using standard MR sequences. MATERIAL AND METHODS: The study had approval by the local ethics commission. One hundred consecutive MR scans in 60 patients at standard follow-up intervals of 1, 3, 6, 12, 24, and 60 months after MACT of the knee joint were prospectively included. The mean follow-up interval of this cross-sectional evaluation was 21.4 +/- 20.6 months; the mean age of the patients was 35.8 +/- 9.4 years. MRI was performed at a 3.0 Tesla unit. All variables of the standard 2D MOCART score where part of the new 3D MOCART score. Furthermore, additional variables and options were included with the aims to use the capabilities of isotropic MRI, to include the results of recent studies, and to adapt to the needs of patients and physician in a clinical routine examination. A proton-density turbo spin-echo sequence, a T2-weighted dual fast spin-echo (dual-FSE) sequence, and a T1-weighted turbo inversion recovery magnitude (TIRM) sequence were used to assess the standard 2D MOCART score; an isotropic 3D-TrueFISP sequence was prepared to evaluate the new 3D MOCART score. All 9 variables of the 2D MOCART score were compared with the corresponding variables obtained by the 3D MOCART score using the Pearson correlation coefficient; additionally the subjective quality and possible artifacts of the MR sequences were analyzed. RESULTS: The correlation between the standard 2D MOCART score and the new 3D MOCART showed for the 8 variables "defect fill," "cartilage interface," "surface," "adhesions," "structure," "signal intensity," "subchondral lamina," and "effusion"-a highly significant (P < 0.001) correlation with a Pearson coefficient between 0.566 and 0.932. The variable "bone marrow edema" correlated significantly (P < 0.05; Pearson coefficient: 0.257). The subjective quality of the 3 standard MR sequences was comparable to the isotropic 3D-TrueFISP sequence. Artifacts were more frequently visible within the 3D-TrueFISP sequence. CONCLUSION: In the clinical routine follow-up after cartilage repair, the 3D MOCART score, assessed by only 1 high-resolution isotropic MR sequence, provides comparable information than the standard 2D MOCART score. Hence, the new 3D MOCART score has the potential to combine the information of the standard 2D MOCART score with the possible advantages of isotropic 3D MRI at high-field. A clear limitation of the 3D-TrueFISP sequence was the high number of artifacts. Future studies have to prove the clinical benefits of a 3D MOCART score.

Evidence for direct squalene and 2,3-oxidosqualene binding by supernatant protein factor

We present the crystal structures of the SEC14-like domain of supernatant protein factor (SPF) in complex with squalene and 2,3-oxidosqualene. The structures were resolved at 1.75 Å (complex with squalene) and 1.6 Å resolution (complex with 2,3-oxidosqualene), leading in both cases to clear images of the protein/ substrate interactions. Ligand binding is facilitated by removal of the Golgi-dynamics (GOLD) C-terminal domain of SPF, which, as shown in previous structures of the apo-protein, blocked the opening of the binding pocket to the exterior. Both substrates bind into a large hydrophobic cavity, typical of such lipid-transporter family. Our structures report no specific recognition mode for the epoxide group. In fact, for both molecules, ligand affinity is dominated by hydrophobic interactions, and independent investigations by computational models or differential scanning micro-calorimetry reveal similar binding affinities for both ligands. Our findings elucidate the molecular bases of the role of SPF in sterol endo-synthesis, supporting the original hypothesis that SPF is a facilitator of substrate flow within the sterol synthetic pathway. Moreover, our results suggest that the GOLD domain acts as a regulator, as its conformational displacement must occur to favor ligand binding and release during the different synthetic steps.

Higher order parametric excitation modes for spaceborne quadrupole mass spectrometers

This paper describes a technique to significantly improve upon the mass peak shape and mass resolution of spaceborne quadrupolemass spectrometers (QMSs) through higher order auxiliary excitation of the quadrupole field. Using a novel multiresonant tank circuit, additional frequency components can be used to drive modulating voltages on the quadrupole rods in a practical manner, suitable for both improved commercial applications and spaceflight instruments. Auxiliary excitation at frequencies near twice that of the fundamental quadrupole RF frequency provides the advantages of previously studied parametric excitation techniques, but with the added benefit of increased sensed excitation amplitude dynamic range and the ability to operate voltage scan lines through the center of upper stability islands. Using a field programmable gate array, the amplitudes and frequencies of all QMS signals are digitally generated and managed, providing a robust and stable voltage control system. These techniques are experimentally verified through an interface with a commercial Pfeiffer QMG422 quadrupole rod system. When operating through the center of a stability island formed from higher order auxiliary excitation, approximately 50% and 400% improvements in 1% mass resolution and peak stability were measured, respectively, when compared with traditional QMS operation. Although tested with a circular rod system, the presented techniques have the potential to improve the performance of both circular and hyperbolic rod geometry QMS sensors.