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Stereocontrolled enantioselective total synthesis of the [2+2] quadrigemine alkaloids
Abstract A unified strategy for enantioselective total synthesis of all stereoisomers of the [2+2] family of quadrigemine alkaloids is reported. In this approach, two enantioselective intramolecular Heck reactions are carried out at the same time on precursors fashioned in four steps from either meso- or (+)-chimonanthine to form the two critical quaternary carbons of the peripheral cyclotryptamine rings of these products. Useful levels of catalyst control are realized in either desymmetrizing a meso precursor or controlling diastereoselectivity in elaborating C2-symmetric intermediates. None of the synthetic quadrigemines are identical with alkaloids isolated previously and referred to as quadrigemines A and E. In addition, we report improvements in our previous total syntheses of (+)- or (-)-quadrigemine C that shortened the synthetic sequence to 10 steps and provided these products in 2.2% overall yield from tryptamine
Early compaction at day 3 may be a useful additional criterion for embryo transfer
PURPOSE: The reduction of the number of embryos transferred while maintaining a satisfactory rate of pregnancy (PR) with in vitro fertilization calls for a refined technique of embryonic selection. This prospective study investigates the significance of early embryonic compaction at day 3 as a marker of the chances of implantation. METHODS: We examined 317 transfers and their outcome involving 509 embryos including 91 compacted embryos. RESULTS: Early compaction seems linked with the ovarian response to stimulation and embryonic quality. The PR is significantly increased when the embryonic cohort contains at least one compacted embryo (44% versus 29.5%, p = 0.01), and when at least one compacted embryo is transferred (44% versus 31%, p < 0.05). The analysis of our single embryo transfers shows that the implantation rates are significantly better for compacted embryos (50% versus 30%, p < 0.05) (OR 2.98; CI 1.02-5.28). CONCLUSION: Thus, early compaction, sometimes observed at day 3, may serve as a useful additional criterion for selecting the embryos transferred
SiO line emission from C-type shock waves : interstellar jets and outflows
We study the production of SiO in the gas phase of molecular outflows,
through the sputtering of Si--bearing material in refractory grain cores, which
are taken to be olivine; we calculate also the rotational line spectrum of the
SiO. The sputtering is driven by neutral particle impact on charged grains, in
steady--state C-type shock waves, at the speed of ambipolar diffusion. The
emission of the SiO molecule is calculated by means of an LVG code. A grid of
models has been generated. We compare our results with those of an earlier
study (Schilke et al. 1997). Improvements in the treatment of the coupling
between the charged grains and the neutral fluid lead to narrower shock waves
and lower fractions of Si being released into the gas phase. More realistic
assumptions concerning the initial fractional abundance of O2 lead to SiO
formation being delayed, so that it occurs in the cool, dense postshock flow.
Good agreement is obtained with recent observations of SiO line intensities in
the L1157 and L1448 molecular outflows. The inferred temperature, opacity, and
SiO column density in the emission region differ significantly from those
estimated by means of LVG `slab' models. The fractional abundance of SiO is
deduced. Observed line profiles are wider than predicted and imply multiple,
unresolved shock regions within the beam.Comment: 1 tex doc, 19 figure
Measuring the Temperature of Hot Nuclear Fragments
A new thermometer based on fragment momentum fluctuations is presented. This
thermometer exhibited residual contamination from the collective motion of the
fragments along the beam axis. For this reason, the transverse direction has
been explored. Additionally, a mass dependence was observed for this
thermometer. This mass dependence may be the result of the Fermi momentum of
nucleons or the different properties of the fragments (binding energy, spin
etc..) which might be more sensitive to different densities and temperatures of
the exploding fragments. We expect some of these aspects to be smaller for
protons (and/or neutrons); consequently, the proton transverse momentum
fluctuations were used to investigate the temperature dependence of the source
Hsp90 governs dispersion and drug resistance of fungal biofilms
Fungal biofilms are a major cause of human mortality and are recalcitrant to most treatments due to intrinsic drug resistance. These complex communities of multiple cell types form on indwelling medical devices and their eradication often requires surgical removal of infected devices. Here we implicate the molecular chaperone Hsp90 as a key regulator of biofilm dispersion and drug resistance. We previously established that in the leading human fungal pathogen, Candida albicans, Hsp90 enables the emergence and maintenance of drug resistance in planktonic conditions by stabilizing the protein phosphatase calcineurin and MAPK Mkc1. Hsp90 also regulates temperature-dependent C. albicans morphogenesis through repression of cAMP-PKA signalling. Here we demonstrate that genetic depletion of Hsp90 reduced C. albicans biofilm growth and maturation in vitro and impaired dispersal of biofilm cells. Further, compromising Hsp90 function in vitro abrogated resistance of C. albicans biofilms to the most widely deployed class of antifungal drugs, the azoles. Depletion of Hsp90 led to reduction of calcineurin and Mkc1 in planktonic but not biofilm conditions, suggesting that Hsp90 regulates drug resistance through different mechanisms in these distinct cellular states. Reduction of Hsp90 levels led to a marked decrease in matrix glucan levels, providing a compelling mechanism through which Hsp90 might regulate biofilm azole resistance. Impairment of Hsp90 function genetically or pharmacologically transformed fluconazole from ineffectual to highly effective in eradicating biofilms in a rat venous catheter infection model. Finally, inhibition of Hsp90 reduced resistance of biofilms of the most lethal mould, Aspergillus fumigatus, to the newest class of antifungals to reach the clinic, the echinocandins. Thus, we establish a novel mechanism regulating biofilm drug resistance and dispersion and that targeting Hsp90 provides a much-needed strategy for improving clinical outcome in the treatment of biofilm infections
Fluctuation scaling in complex systems: Taylor's law and beyond
Complex systems consist of many interacting elements which participate in
some dynamical process. The activity of various elements is often different and
the fluctuation in the activity of an element grows monotonically with the
average activity. This relationship is often of the form "", where the exponent is predominantly in
the range . This power law has been observed in a very wide range of
disciplines, ranging from population dynamics through the Internet to the stock
market and it is often treated under the names \emph{Taylor's law} or
\emph{fluctuation scaling}. This review attempts to show how general the above
scaling relationship is by surveying the literature, as well as by reporting
some new empirical data and model calculations. We also show some basic
principles that can underlie the generality of the phenomenon. This is followed
by a mean-field framework based on sums of random variables. In this context
the emergence of fluctuation scaling is equivalent to some corresponding limit
theorems. In certain physical systems fluctuation scaling can be related to
finite size scaling.Comment: 33 pages, 20 figures, 2 tables, submitted to Advances in Physic
Flight of the dragonflies and damselflies
This work is a synthesis of our current understanding of the mechanics, aerodynamics and visually mediated control of dragonfly and damselfly flight, with the addition of new experimental and computational data in several key areas. These are: the diversity of dragonfly wing morphologies, the aerodynamics of gliding flight, force generation in flapping flight, aerodynamic efficiency, comparative flight performance and pursuit strategies during predatory and territorial flights. New data are set in context by brief reviews covering anatomy at several scales, insect aerodynamics, neuromechanics and behaviour. We achieve a new perspective by means of a diverse range of techniques, including laser-line mapping of wing topographies, computational fluid dynamics simulations of finely detailed wing geometries, quantitative imaging using particle image velocimetry of on-wing and wake flow patterns, classical aerodynamic theory, photography in the field, infrared motion capture and multi-camera optical tracking of free flight trajectories in laboratory environments. Our comprehensive approach enables a novel synthesis of datasets and subfields that integrates many aspects of flight from the neurobiology of the compound eye, through the aeromechanical interface with the surrounding fluid, to flight performance under cruising and higher-energy behavioural modes
Central modulation in cluster headache patients treated with occipital nerve stimulation: an FDG-PET study
Peer reviewe
Intercomparison of the northern hemisphere winter mid-latitude atmospheric variability of the IPCC models
We compare, for the overlapping time frame 1962-2000, the estimate of the
northern hemisphere (NH) mid-latitude winter atmospheric variability within the
XX century simulations of 17 global climate models (GCMs) included in the
IPCC-4AR with the NCEP and ECMWF reanalyses. We compute the Hayashi spectra of
the 500hPa geopotential height fields and introduce an integral measure of the
variability observed in the NH on different spectral sub-domains. Only two
high-resolution GCMs have a good agreement with reanalyses. Large biases, in
most cases larger than 20%, are found between the wave climatologies of most
GCMs and the reanalyses, with a relative span of around 50%. The travelling
baroclinic waves are usually overestimated, while the planetary waves are
usually underestimated, in agreement with previous studies performed on global
weather forecasting models. When comparing the results of various versions of
similar GCMs, it is clear that in some cases the vertical resolution of the
atmosphere and, somewhat unexpectedly, of the adopted ocean model seem to be
critical in determining the agreement with the reanalyses. The GCMs ensemble is
biased with respect to the reanalyses but is comparable to the best 5 GCMs.
This study suggests serious caveats with respect to the ability of most of the
presently available GCMs in representing the statistics of the global scale
atmospheric dynamics of the present climate and, a fortiori, in the perspective
of modelling climate change.Comment: 39 pages, 8 figures, 2 table
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