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Conformational modulation of sequence recognition in synthetic macromolecules
The different triplet sequences in high molecular weight aromatic copolyimides comprising pyromellitimide units ("I") flanked by either ether-ketone ("K") or ether-sulfone residues ("S") show different binding strengths for pyrene-based tweezer-molecules. Such molecules bind primarily to the diimide unit through complementary π-π-stacking and hydrogen bonding. However, as shown by the magnitudes of 1H NMR complexation shifts and tweezer-polymer binding constants, the triplet "SIS" binds tweezer-molecules more strongly than "KIS" which in turn bind such molecules more strongly than "KIK". Computational models for tweezer-polymer binding, together with single-crystal X-ray analyses of tweezer-complexes with macrocyclic ether-imides, reveal that the variations in binding strength between the different triplet sequences arise from the different conformational preferences of aromatic rings at diarylketone and diarylsulfone linkages. These preferences determine whether or not chain-folding and secondary π−π-stacking occurs between the arms of the tweezermolecule and the 4,4'-biphenylene units which flank the central diimide residue
Patterns of differential introgression in a salamander hybrid zone: inferences from genetic data and ecological niche modelling
Hybrid zones have yielded considerable insight into many evolutionary processes, including speciation and the maintenance of species boundaries. Presented here are analyses from a hybrid zone that occurs among three salamanders – Plethodon jordani , Plethodon metcalfi and Plethodon teyahalee – from the southern Appalachian Mountains. Using a novel statistical approach for analysis of non-clinal, multispecies hybrid zones, we examined spatial patterns of variation at four markers: single-nucleotide polymorphisms (SNPs) located in the mtDNA ND2 gene and the nuclear DNA ILF3 gene, and the morphological markers of red cheek pigmentation and white flecks. Concordance of the ILF3 marker and both morphological markers across four transects is observed. In three of the four transects, however, the pattern of mtDNA is discordant from all other markers, with a higher representation of P. metcalfi mtDNA in the northern and lower elevation localities than is expected given the ILF3 marker and morphology. To explore whether climate plays a role in the position of the hybrid zone, we created ecological niche models for P. jordani and P. metcalfi . Modelling results suggest that hybrid zone position is not determined by steep gradients in climatic suitability for either species. Instead, the hybrid zone lies in a climatically homogenous region that is broadly suitable for both P. jordani and P. metcalfi . We discuss various selective (natural selection associated with climate) and behavioural processes (sex-biased dispersal, asymmetric reproductive isolation) that might explain the discordance in the extent to which mtDNA and nuclear DNA and colour-pattern traits have moved across this hybrid zone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79135/1/j.1365-294X.2010.04796.x.pd
Analytical response time estimation in parallel relational database systems
Techniques for performance estimation in parallel database systems are well established for parameters such as throughput, bottlenecks and resource utilisation. However, response time estimation is a complex activity which is difficult to predict and has attracted research for a number of years. Simulation is one option for predicting response time but this is a costly process. Analytical modelling is a less expensive option but requires approximations and assumptions about the queueing networks built up in real parallel database machines which are often questionable and few of the papers on analytical approaches are backed by results from validation against real machines. This paper describes a new analytical approach for response time estimation that is based on a detailed study of different approaches and assumptions. The approach has been validated against two commercial parallel DBMSs running on actual parallel machines and is shown to produce acceptable accuracy
Organic Carbon, Inorganic Carbon, and Related Variables in Offshore Oil Production Areas of the Northern Gulf of Mexico
Paper by Charles R. Brent, Howard P. Williams, W. A. Bergin, John L. Tyvoll, and Tommy E. Myer
The autonomic brain: Multi-dimensional generative hierarchical modelling of the autonomic connectome.
The autonomic nervous system governs the body's multifaceted internal adaptation to diverse changes in the external environment, a role more complex than is accessible to the methods-and data scales-hitherto used to illuminate its operation. Here we apply generative graphical modelling to large-scale multimodal neuroimaging data encompassing normal and abnormal states to derive a comprehensive hierarchical representation of the autonomic brain. We demonstrate that whereas conventional structural and functional maps identify regions jointly modulated by parasympathetic and sympathetic systems, only graphical analysis discriminates between them, revealing the cardinal roles of the autonomic system to be mediated by high-level distributed interactions. We provide a novel representation of the autonomic system-a multidimensional, generative network-that renders its richness tractable within future models of its function in health and disease
The need for increased protection of Antarctica's inland waters
Protection of Antarctica's biodiversity and ecosystem values is enshrined in the Protocol on Environmental Protection to the Antarctic Treaty, which provides for the designation of Antarctic Specially Protected Areas (ASPAs) to areas with outstanding values. Concern has been raised that existing ASPAs fail to prioritize areas to maximize the likelihood of ensuring the long-term conservation of Antarctic ecosystems and biodiversity. The absence of systematic and representative protection is particularly acute for inland aquatic ecosystems, which support a disproportionate amount of inland biodiversity. This paper promotes the case for overt inclusion of inland waters as a critical component of a representative protected area framework for Antarctica, thereby addressing their current underrepresentation. We set out a structured approach to enable the selection of representative freshwater systems for inclusion in the ASPA framework that, with modification, could also be applied across other Antarctic habitats. We acknowledge an overall lack of information on the biogeography of inland aquatic diversity and recommend increased use of remote data collection along with classification tools to mitigate this, as well as the need for the consideration of catchment-scale processes. Changes that accompany contemporary and anticipated climate change make the need for the conservation of representative biodiversity increasingly urgen
The autonomic brain: multi-dimensional generative hierarchical modelling of the autonomic connectome
The autonomic nervous system governs the body's multifaceted internal adaptation to diverse changes in the external environment, a role more complex than is accessible to the methods — and data scales — hitherto used to illuminate its operation. Here we apply generative graphical modelling to large-scale multimodal neuroimaging data encompassing normal and abnormal states to derive a comprehensive hierarchical representation of the autonomic brain. We demonstrate that whereas conventional structural and functional maps identify regions jointly modulated by parasympathetic and sympathetic systems, only graphical analysis discriminates between them, revealing the cardinal roles of the autonomic system to be mediated by high-level distributed interactions. We provide a novel representation of the autonomic system — a multidimensional, generative network — that renders its richness tractable within future models of its function in health and disease
Effect of Solar Wind Drag on the Determination of the Properties of Coronal Mass Ejections from Heliospheric Images
The Fixed-\Phi (F\Phi) and Harmonic Mean (HM) fitting methods are two methods
to determine the average direction and velocity of coronal mass ejections
(CMEs) from time-elongation tracks produced by Heliospheric Imagers (HIs), such
as the HIs onboard the STEREO spacecraft. Both methods assume a constant
velocity in their descriptions of the time-elongation profiles of CMEs, which
are used to fit the observed time-elongation data. Here, we analyze the effect
of aerodynamic drag on CMEs propagating through interplanetary space, and how
this drag affects the result of the F\Phi and HM fitting methods. A simple drag
model is used to analytically construct time-elongation profiles which are then
fitted with the two methods. It is found that higher angles and velocities give
rise to greater error in both methods, reaching errors in the direction of
propagation of up to 15 deg and 30 deg for the F\Phi and HM fitting methods,
respectively. This is due to the physical accelerations of the CMEs being
interpreted as geometrical accelerations by the fitting methods. Because of the
geometrical definition of the HM fitting method, it is affected by the
acceleration more greatly than the F\Phi fitting method. Overall, we find that
both techniques overestimate the initial (and final) velocity and direction for
fast CMEs propagating beyond 90 deg from the Sun-spacecraft line, meaning that
arrival times at 1 AU would be predicted early (by up to 12 hours). We also
find that the direction and arrival time of a wide and decelerating CME can be
better reproduced by the F\Phi due to the cancellation of two errors:
neglecting the CME width and neglecting the CME deceleration. Overall, the
inaccuracies of the two fitting methods are expected to play an important role
in the prediction of CME hit and arrival times as we head towards solar maximum
and the STEREO spacecraft further move behind the Sun.Comment: Solar Physics, Online First, 17 page
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