5,696 research outputs found
Data processing method for a weak, moving telemetry signal
Method of processing data from a spacecraft, where the carrier has a low signal-to-noise ratio and wide unpredictable frequency shifts, consists of analogue recording of the noisy signal along with a high-frequency tone that is used as a clock to trigger a digitizer
DNA: From rigid base-pairs to semiflexible polymers
The sequence-dependent elasticity of double-helical DNA on a nm length scale
can be captured by the rigid base-pair model, whose strains are the relative
position and orientation of adjacent base-pairs. Corresponding elastic
potentials have been obtained from all-atom MD simulation and from
high-resolution structural data. On the scale of a hundred nm, DNA is
successfully described by a continuous worm-like chain model with homogeneous
elastic properties characterized by a set of four elastic constants, which have
been directly measured in single-molecule experiments. We present here a theory
that links these experiments on different scales, by systematically
coarse-graining the rigid base-pair model for random sequence DNA to an
effective worm-like chain description. The average helical geometry of the
molecule is exactly taken into account in our approach. We find that the
available microscopic parameters sets predict qualitatively similar mesoscopic
parameters. The thermal bending and twisting persistence lengths computed from
MD data are 42 and 48 nm, respectively. The static persistence lengths are
generally much higher, in agreement with cyclization experiments. All
microscopic parameter sets predict negative twist-stretch coupling. The
variability and anisotropy of bending stiffness in short random chains lead to
non-Gaussian bend angle distributions, but become unimportant after two helical
turns.Comment: 13 pages, 6 figures, 6 table
A note on Turán type and mean inequalities for the Kummer function
AbstractTurán-type inequalities for combinations of Kummer functions involving Φ(a±ν,c±ν,x) and Φ(a,c±ν,x) have been recently investigated in [Á. Baricz, Functional inequalities involving Bessel and modified Bessel functions of the first kind, Expo. Math. 26 (3) (2008) 279–293; M.E.H. Ismail, A. Laforgia, Monotonicity properties of determinants of special functions, Constr. Approx. 26 (2007) 1–9]. In the current paper, we resolve the corresponding Turán-type and closely related mean inequalities for the additional case involving Φ(a±ν,c,x). The application to modeling credit risk is also summarized
Emerging Technologies for the Production of Renewable Liquid Transport Fuels from Biomass Sources Enriched in Plant Cell Walls
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.Plant cell walls are composed predominantly of cellulose, a range of non-cellulosic polysaccharides and lignin. The walls account for a large proportion not only of crop residues such as wheat straw and sugarcane bagasse, but also of residues of the timber industry and specialist grasses and other plants being grown specifically for biofuel production. The polysaccharide components of plant cell walls have long been recognized as an extraordinarily large source of fermentable sugars that might be used for the production of bioethanol and other renewable liquid transport fuels. Estimates place annual plant cellulose production from captured light energy in the order of hundreds of billions of tons. Lignin is synthesized in the same order of magnitude and, as a very large polymer of phenylpropanoid residues, lignin is also an abundant, high energy macromolecule. However, one of the major functions of these cell wall constituents in plants is to provide the extreme tensile and compressive strengths that enable plants to resist the forces of gravity and a broad range of other mechanical forces. Over millions of years these wall constituents have evolved under natural selection to generate extremely tough and resilient biomaterials. The rapid degradation of these tough cell wall composites to fermentable sugars is therefore a difficult task and has significantly slowed the development of a viable lignocellulose-based biofuels industry. However, good progress has been made in overcoming this so-called recalcitrance of lignocellulosic feedstocks for the biofuels industry, through modifications to the lignocellulose itself, innovative pre-treatments of the biomass, improved enzymes and the development of superior yeasts and other microorganisms for the fermentation process. Nevertheless, it has been argued that bioethanol might not be the best or only biofuel that can be generated from lignocellulosic biomass sources and that hydrocarbons with intrinsically higher energy densities might be produced using emerging and continuous flow systems that are capable of converting a broad range of plant and other biomasses to bio-oils through so-called ‘agnostic’ technologies such as hydrothermal liquefaction. Continued attention to regulatory frameworks and ongoing government support will be required for the next phase of development of internationally viable biofuels industries
Granger causality and transfer entropy are equivalent for Gaussian variables
Granger causality is a statistical notion of causal influence based on
prediction via vector autoregression. Developed originally in the field of
econometrics, it has since found application in a broader arena, particularly
in neuroscience. More recently transfer entropy, an information-theoretic
measure of time-directed information transfer between jointly dependent
processes, has gained traction in a similarly wide field. While it has been
recognized that the two concepts must be related, the exact relationship has
until now not been formally described. Here we show that for Gaussian
variables, Granger causality and transfer entropy are entirely equivalent, thus
bridging autoregressive and information-theoretic approaches to data-driven
causal inference.Comment: In review, Phys. Rev. Lett., Nov. 200
The Hudson Bay Lithospheric Experiment (HuBLE) : Insights into Precambrian Plate Tectonics and the Development of Mantle Keels
The UK component of HuBLE was supported by Natural Environment Research Council (NERC) grant NE/F007337/1, with financial and logistical support from the Geological Survey of Canada, Canada–Nunavut Geoscience Office, SEIS-UK (the seismic node of NERC), and First Nations communities of Nunavut. J. Beauchesne and J. Kendall provided invaluable assistance in the field. Discussions with M. St-Onge, T. Skulski, D. Corrigan and M. Sanborne-Barrie were helpful for interpretation of the data. D. Eaton and F. A. Darbyshire acknowledge the Natural Sciences and Engineering Research Council. Four stations on the Belcher Islands and northern Quebec were installed by the University of Western Ontario and funded through a grant to D. Eaton (UWO Academic Development Fund). I. Bastow is funded by the Leverhulme Trust. This is Natural Resources Canada Contribution 20130084 to its Geomapping for Energy and Minerals Program. This work has received funding from the European Research Council under the European Unions Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement no. 240473 ‘CoMITAC’.Peer reviewedPublisher PD
Letter from W. H. Elson, Edwin B. Cox, C. N. Kendall, F. T. Oldt, and A. W. Rankin
Letter concerning resolutions being voted on concerning the National Educational Association
Maximum-likelihood absorption tomography
Maximum-likelihood methods are applied to the problem of absorption
tomography. The reconstruction is done with the help of an iterative algorithm.
We show how the statistics of the illuminating beam can be incorporated into
the reconstruction. The proposed reconstruction method can be considered as a
useful alternative in the extreme cases where the standard ill-posed
direct-inversion methods fail.Comment: 7 pages, 5 figure
Spatiotemporal complexity of a ratio-dependent predator-prey system
In this paper, we investigate the emergence of a ratio-dependent
predator-prey system with Michaelis-Menten-type functional response and
reaction-diffusion. We derive the conditions for Hopf, Turing and Wave
bifurcation on a spatial domain. Furthermore, we present a theoretical analysis
of evolutionary processes that involves organisms distribution and their
interaction of spatially distributed population with local diffusion. The
results of numerical simulations reveal that the typical dynamics of population
density variation is the formation of isolated groups, i.e., stripelike or
spotted or coexistence of both. Our study shows that the spatially extended
model has not only more complex dynamic patterns in the space, but also chaos
and spiral waves. It may help us better understand the dynamics of an aquatic
community in a real marine environment.Comment: 6pages, revtex
On the nature of surface roughness with application to contact mechanics, sealing, rubber friction and adhesion
Surface roughness has a huge impact on many important phenomena. The most
important property of rough surfaces is the surface roughness power spectrum
C(q). We present surface roughness power spectra of many surfaces of practical
importance, obtained from the surface height profile measured using optical
methods and the Atomic Force Microscope. We show how the power spectrum
determines the contact area between two solids. We also present applications to
sealing, rubber friction and adhesion for rough surfaces, where the power
spectrum enters as an important input.Comment: Topical review; 82 pages, 61 figures; Format: Latex (iopart). Some
figures are in Postscript Level
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