288 research outputs found
Stabilizing a Molecular Switch at Solid Surfaces: A Density-Functional Theory Study of Azobenzene at Cu(111), Ag(111), and Au(111)
We present a density-functional theory trend study addressing the binding of
the trans-cis conformational switch azobenzene (C6H5-N=N-C6H5) at three coinage
metal surfaces. From the reported detailed energetic, geometric, and electronic
structure data we conclude that the governing factor for the molecule-surface
interaction is a competition between covalent bonding of the central azo
(-N=N-) bridge on the one hand and the surface interaction of the two
closed-shell phenyl (-C6H5) rings on the other. With respect to this factor the
cis conformer exhibits a more favorable gas-phase geometric structure and is
thus more stabilized at the studied surfaces. With the overall binding still
rather weak the relative stability of the two isomers is thereby reduced at
Ag(111) and Au(111). This is significantly different at Cu(111), where the cis
bonding is strong enough to even reverse the gas-phase energetic order at the
level of the employed semi-local electronic exchange and correlation (xc)
functional. While this actual reversal may well be affected by the deficiencies
due to the approximate xc treatment, we critically discuss that the
rationalization of the general effect of the surface on the meta-stable
molecular states is quite robust. This should equally hold for the presented
analysis of recent tip-manipulation and photo-excitation isomerization
experiments from the view point of the derived bonding mechanism.Comment: 10 pages including 4 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Azobenzene versus 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) at Au(111): Characterizing the role of spacer groups
We present large-scale density-functional theory (DFT) calculations and
temperature programmed desorption measurements to characterize the structural,
energetic and vibrational properties of the functionalized molecular switch
3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) adsorbed at Au(111). Particular
emphasis is placed on exploring the accuracy of the semi-empirical dispersion
correction approach to semi-local DFT (DFT-D) in accounting for the substantial
van der Waals component in the surface chemical bond. In line with previous
findings for benzene and pure azobenzene at coinage metal surfaces, DFT-D
significantly overbinds the molecule, but seems to yield an accurate adsorption
geometry as far as can be judged from the experimental data. Comparing the
trans adsorption geometry of TBA and azobenzene at Au(111) reveals a remarkable
insensitivity of the structural and vibrational properties of the -N=N- moiety.
This questions the established view of the role of the bulky tert-butyl-spacer
groups for the switching of TBA in terms of a mere geometric decoupling of the
photochemically active diazo-bridge from the gold substrate.Comment: 9 pages including 6 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Waterborne Toxoplasmosis, Northeastern Brazil
Two waterborne outbreaks of toxoplasmosis have been described recently in southern Brazil. We present data from a community-based study of pregnant women in northeastern Brazil. Consumption of homemade ice was the only variable associated with seropositivity (adjusted odds ratio, 3.1, 95% confidence interval, 1.53–6.24). Our results suggest water as a source of infection with Toxoplasma gondii
Creating Calibration Curves to Determine Shock Pressure in Clinopyroxene
Impact cratering is an important geological process that occurs on every rocky body in the solar system. It alters the texture and mineralogy of rocks via shock metamorphism. The peak shock pressures experienced by a rock are traditionally evaluated using qualitative optical methods however, quantitative methods do exist. One such method was developed by Uchizono et al., who used X-ray Diffraction (XRD) to measure lattice strain () in several artificially shocked olivine grains using XRD peak broadening as a function of tan , where is the diffraction angle. They plotted the values against the known peak shock pressures experienced by the olivine grains. Using this calibration curve, the precise shock pressure experienced by a grain of olivine can be determined using its measured value. Another method was developed by McCausland et al. and Izawa et al., who used in situ XRD to measure strain-related mosaicity (SRM) of olivine in several ordinary chondrites and enstatite in enstatite chondrites, respectively. They plotted these results against the shock stage estimates for these meteorites. Using these plots, meteorites can be assigned to shock stage bins by measuring the SRM of olivine and/or enstatite. Both methods are useful for evaluating shock metamorphism, however, they have limitations. Uchizono et al.s calibration curve has been successfully applied to martian meteorites, however it can only be applied to olivine-bearing rocks. McCausland et al.s and Izawa et al.s SRM method is uncalibrated and is limited to binning meteorites by shock stage. This work aims to expand on both methods by creating calibration curves for clinopyroxene (CPX): one for , similar to Uchizono et al.s calibration curve for olivine, and one for SRM. This will extend the application of shock calibration methods to a greater variety of rock types. Preliminary results are presented herein
Ruling out Stellar Companions and Resolving the Innermost Regions of Transitional Disks with the Keck Interferometer
With the Keck Interferometer, we have studied at 2 um the innermost regions
of several nearby, young, dust depleted "transitional" disks. Our observations
target five of the six clearest cases of transitional disks in the
Taurus/Auriga star-forming region (DM Tau, GM Aur, LkCa 15, UX Tau A, and RY
Tau) to explore the possibility that the depletion of optically thick dust from
the inner disks is caused by stellar companions rather than the more typical
planet-formation hypothesis. At the 99.7% confidence level, the observed
visibilities exclude binaries with flux ratios of at least 0.05 and separations
ranging from 2.5 to 30 mas (0.35 - 4 AU) over >= 94% of the area covered by our
measurements. All targets but DM Tau show near-infrared excess in their SED
higher than our companion flux ratio detection limits. While a companion has
previously been detected in the candidate transitional disk system CoKu Tau/4,
we can exclude similar mass companions as the typical origin for the clearing
of inner dust in transitional disks and of the near-infrared excess emission.
Unlike CoKu Tau/4, all our targets show some evidence of accretion. We find
that all but one of the targets are clearly spatially resolved, and UX Tau A is
marginally resolved. Our data is consistent with hot material on small scales
(0.1 AU) inside of and separated from the cooler outer disk, consistent with
the recent SED modeling. These observations support the notion that some
transitional disks have radial gaps in their optically thick material, which
could be an indication for planet formation in the habitable zone (~ a few AU)
of a protoplanetary disk.Comment: 36 pages, 7 figures. Accepted for publication in Ap
A direct-to-drive neural data acquisition system
Driven by the increasing channel count of neural probes, there is much effort being directed to creating increasingly scalable electrophysiology data acquisition (DAQ) systems. However, all such systems still rely on personal computers for data storage, and thus are limited by the bandwidth and cost of the computers, especially as the scale of recording increases. Here we present a novel architecture in which a digital processor receives data from an analog-to-digital converter, and writes that data directly to hard drives, without the need for a personal computer to serve as an intermediary in the DAQ process. This minimalist architecture may support exceptionally high data throughput, without incurring costs to support unnecessary hardware and overhead associated with personal computers, thus facilitating scaling of electrophysiological recording in the future.National Institutes of Health (U.S.) (Grant 1DP1NS087724)National Institutes of Health (U.S.) (Grant 1R01DA029639)National Institutes of Health (U.S.) (Grant 1R01NS067199)National Institutes of Health (U.S.) (Grant 2R44NS070453)National Institutes of Health (U.S.) (Grant R43MH101943)New York Stem Cell FoundationPaul Allen FoundationMassachusetts Institute of Technology. Media LaboratoryGoogle (Firm)United States. Defense Advanced Research Projects Agency (HR0011-14-2-0004)Hertz Foundation (Myhrvold Family Fellowship
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The Genome of the Epsilonproteobacterial Chemolithoautotroph Sulfurimonas dentrificans
Sulfur-oxidizing epsilonproteobacteria are common in a variety of sulfidogenic environments. These autotrophic and mixotrophic sulfur-oxidizing bacteria are believed to contribute substantially to the oxidative portion of the global sulfur cycle. In order to better understand the ecology and roles of sulfur-oxidizing epsilonproteobacteria, in particular those of the widespread genus Sulfurimonas, in biogeochemical cycles, the genome of Sulfurimonas denitrificans DSM1251 was sequenced. This genome has many features, including a larger size (2.2 Mbp), that suggest a greater degree of metabolic versatility or responsiveness to the environment than seen for most of the other sequenced epsilonproteobacteria. A branched electron transport chain is apparent, with genes encoding complexes for the oxidation of hydrogen, reduced sulfur compounds, and formate and the reduction of nitrate and oxygen. Genes are present for a complete, autotrophic reductive citric acid cycle. Many genes are present that could facilitate growth in the spatially and temporally heterogeneous sediment habitat from where Sulfurimonas denitrificans was originally isolated. Many resistance-nodulation-development family transporter genes (10 total) are present; of these, several are predicted to encode heavy metal efflux transporters. An elaborate arsenal of sensory and regulatory protein-encoding genes is in place, as are genes necessary to prevent and respond to oxidative stress
Biodiversity post-2020: Closing the gap between global targets and national-level implementation
National and local governments need to step up efforts to effectively implement the post-2020 global biodiversity framework of the Convention on Biological Diversity to halt and reverse worsening biodiversity trends. Drawing on recent advances in interdisciplinary biodiversity science, we propose a framework for improved implementation by national and subnational governments. First, the identification of actions and the promotion of ownership across stakeholders need to recognize the multiple values of biodiversity and account for remote responsibility. Second, cross-sectorial implementation and mainstreaming should adopt scalable and multifunctional ecosystem restoration approaches and target positive futures for nature and people. Third, assessment of progress and adaptive management can be informed by novel biodiversity monitoring and modeling approaches handling the multidimensionality of biodiversity change
Progress in upscaling Miscanthus biomass production for the European bio-economy with seed-based hybrids
Funded by UK's Biotechnology and Biological Sciences Research Council (BBSRC) Department for Environment, Food and Rural Affairs (DEFRA). Grant Number: LK0863 BBSRC strategic programme Grant on Energy Grasses & Bio-refining. Grant Number: BBS/E/W/10963A01 OPTIMISC. Grant Number: FP7-289159 WATBIO. Grant Number: FP7-311929 Innovate UK/BBSRC ‘MUST’. Grant Number: BB/N016149/1Peer reviewedPublisher PD
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