Influence of nonuniform critical current density profile on magnetic field behavior of AC susceptibility in 2D Josephson Junction Arrays

Employing mutual-inductance measurements we study the magnetic field dependence of complex AC susceptibility of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays of unshunted Nb-AlO_x-Nb junctions. The observed behavior can be explained assuming single-plaquette approximation of the overdamped model with an inhomogeneous critical current distribution within a single junction.Comment: 4 pages (REVTEX), 6 figure

Positive Feedback Keeps Duration of Mitosis Temporally Insulated from Upstream Cell-Cycle Events

Cell division is characterized by a sequence of events by which a cell gives rise to two daughter cells. Quantitative measurements of cell-cycle dynamics in single cells showed that despite variability in G1-, S-, and G2 phases, duration of mitosis is short and remarkably constant. Surprisingly, there is no correlation between cell-cycle length and mitotic duration, suggesting that mitosis is temporally insulated from variability in earlier cell-cycle phases. By combining live cell imaging and computational modeling, we showed that positive feedback is the molecular mechanism underlying the temporal insulation of mitosis. Perturbing positive feedback gave rise to a sluggish, variable entry and progression through mitosis and uncoupled duration of mitosis from variability in cell cycle length. We show that positive feedback is important to keep mitosis short, constant, and temporally insulated and anticipate it might be a commonly used regulatory strategy to create modularity in other biological systems

Cerebral and cardiovascular effects of analgesic doses of ketamine during a target controlled general anesthesia: a prospective randomized study

Introduction: Ketamine is increasingly being used in various pain settings. The purpose of this study was to assess the effect of an analgesic dose of ketamine in the bispectral index (BIS), spectral edge frequency (SEF-95), density spectral array (DSA), cerebral oximetry (rSO2) and mean arterial pressure (MAP) during general anaesthesia with a target controlled infusion. Methods: A prospective, single-blinded and randomized study on adult patients scheduled for elective spine surgery was carried out. After anaesthesia induction with propofol, remifentanil and rocuronium, when a stable BIS value (45-55) was achieved, an automatic recording of BIS, SEF-95, rSO2 and MAP values during 9 min was performed to establish patients baseline values. Subsequently, patients were randomly assigned to receive a ketamine bolus dose of 0.2 mg/kg, 0.5 mg/kg or 1 mg/kg; all variables were recorded for additional 9 min after the ketamine bolus, in the absence of any surgical stimulus. A p-value <0.05 was considered significant in the statistical analysis. Results and discussion: Thirty-nine patients were enrolled in the study. Our results show a dose-related increase of SEF-95 and BIS values. DSA demonstrate a shift in the frequency range and power distribution towards higher frequencies. Our results do not show significant differences in MAP and rSO2 values. Conclusion: When ketamine is used intraoperatively in analgesic doses, the anaesthetist should anticipate an increase in SEF-95 and BIS values which will not be associated with the level of anaesthesia.info:eu-repo/semantics/publishedVersio