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Theory of constraints

Ben A Ward, Emilio Marañón, Boris Sauterey, Jonathan Rault, David Claessen
Rates of metabolism and population growth are often assumed to decrease universally with increasing organism size. Recent observations have shown, however, that maximum population growth rates among phytoplankton smaller than ∼6 μm in diameter tend to increase with organism size. Here we bring together observations and theory to demonstrate that the observed change in slope is attributable to a trade-off between nutrient uptake and the potential rate of internal metabolism. Specifically, we apply an established model of phytoplankton growth to explore a trade-off between the ability of cells to replenish their internal quota (which increases with size) and their ability to synthesize new biomass (which decreases with size)...
February 2017: American Naturalist
Zhengkang Zhang
W boson pair production processes at e^{+}e^{-} and pp colliders have been conventionally interpreted as measurements of WWZ and WWγ triple gauge couplings (TGCs). Such an interpretation is based on the assumption that new physics effects other than anomalous TGCs are negligible. While this "TGC dominance assumption" was well motivated and useful at LEP2 thanks to precision electroweak constraints, it is already challenged by recent LHC data. In fact, contributions from anomalous Z boson couplings that are allowed by electroweak precision data but neglected in LHC analyses, which are enhanced at high energy, can even dominate over those from the anomalous TGCs considered...
January 6, 2017: Physical Review Letters
Tomas Jonsson
1.The Metabolic Theory of Ecology (MTE) predicts observed patterns in ecology based on metabolic rates of individuals. The theory is influential but also criticized for a lack of firm empirical evidence confirming MTE's quantitative predictions of processes, e.g. outcome of competition, at population or community level. 2.Self-thinning is a well-known population level phenomenon among plants, but a much less studied phenomenon in animal populations and no consensus exists on what a universal thinning slope for animal populations might be, or if it exists...
January 19, 2017: Journal of Animal Ecology
M Pérez-Rodríguez, A Vidal-Vidal, J M Míguez, F J Blas, J-P Torré, M M Piñeiro
Carbon dioxide (CO2) molecules show a rich orientation landscape when they are enclathrated in type I hydrates. Previous studies have described experimentally their preferential orientations, and some theoretical works have explained, but only partially, these experimental results. In the present paper, we use classical molecular dynamics and electronic density functional theory to advance in the theoretical description of CO2 orientations within type I hydrates. Our results are fully compatible with those previously reported, both theoretical and experimental, the geometric shape of the cavities in hydrate being, and therefore, the steric constraints, responsible for some (but not all) preferential angles...
January 16, 2017: Physical Chemistry Chemical Physics: PCCP
Kory M Evans, Brandon T Waltz, Victor A Tagliacollo, Brian L Sidlauskas, James S Albert
In theory, evolutionary modularity allows anatomical structures to respond differently to selective regimes, thus promoting morphological diversification. These differences can then influence the rate and direction of phenotypic evolution among structures. Here we use geometric morphometrics and phenotypic matrix statistics to compare rates of craniofacial evolution and estimate evolvability in the face and braincase modules of a clade of teleost fishes (Gymnotiformes) and a clade of mammals (Carnivora), both of which exhibit substantial craniofacial diversity...
January 16, 2017: Scientific Reports
Francesco Mancarella, John S Wettlaufer
The importance of surface tension effects is being recognized in the context of soft composite solids, where they are found to significantly affect the mechanical properties, such as the elastic response to an external stress. It has recently been discovered that Eshelby's inclusion theory breaks down when the inclusion size approaches the elastocapillary length L ≡ γ/E, where γ is the inclusion/host surface tension and E is the host Young's modulus. Extending our recent results for liquid inclusions, here we model the elastic behavior of a non-dilute distribution of isotropic elastic spherical inclusions in a soft isotropic elastic matrix, subject to a prescribed infinitesimal far-field loading...
January 12, 2017: Soft Matter
Marianne Pasanen-Mortensen, Bodil Elmhagen, Harto Lindén, Roger Bergström, Märtha Wallgren, Ype van der Velde, Sara A O Cousins
Apex predators may buffer bottom-up driven ecosystem change, as top-down suppression may dampen herbivore and mesopredator responses to increased resource availability. However, theory suggests that for this buffering capacity to be realized, the equilibrium abundance of apex predators must increase. This raises the question: will apex predators maintain herbivore/mesopredator limitation, if bottom-up change relaxes resource constraints? Here, we explore changes in mesopredator (red fox Vulpes vulpes) abundance over 220 years in response to eradication and recovery of an apex predator (Eurasian lynx Lynx lynx), and changes in land use and climate which are linked to resource availability...
January 11, 2017: Journal of Animal Ecology
Corrina Moucheraud, Amee Schwitters, Chantelle Boudreaux, Denise Giles, Peter H Kilmarx, Ntolo Ntolo, Zwashe Bangani, Michael E St Louis, Thomas J Bossert
BACKGROUND: Health information systems are central to strong health systems. They assist with patient and program management, quality improvement, disease surveillance, and strategic use of information. Many donors have worked to improve health information systems, particularly by supporting the introduction of electronic health information systems (EHIS), which are considered more responsive and more efficient than older, paper-based systems. As many donor-driven programs are increasing their focus on country ownership, sustainability of these investments is a key concern...
January 10, 2017: BMC Health Services Research
Samuel R Hinton, Eyal Kazin, Tamara M Davis, Chris Blake, Sarah Brough, Matthew Colless, Warrick J Couch, Michael J Drinkwater, Karl Glazebrook, Russell J Jurek, David Parkinson, Kevin A Pimbblet, Gregory B Poole, Michael Pracy, David Woods
We present results from the 2D anisotropic baryon acoustic oscillation (BAO) signal present in the final data set from the WiggleZ Dark Energy Survey. We analyse the WiggleZ data in two ways: first using the full shape of the 2D correlation function and secondly focusing only on the position of the BAO peak in the reconstructed data set. When fitting for the full shape of the 2D correlation function we use a multipole expansion to compare with theory. When we use the reconstructed data we marginalize over the shape and just measure the position of the BAO peak, analysing the data in wedges separating the signal along the line of sight from that parallel to the line of sight...
February 1, 2017: Monthly Notices of the Royal Astronomical Society
Y Xu, J Zhang, Y S Li, Y J Yu, X C Hong, Q M Zhang, S Y Li
We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of YbMgGaO_{4}, which was recently argued to be a promising candidate for a quantum spin liquid (QSL). In a zero magnetic field, a large magnetic contribution of specific heat is observed, and exhibits a power-law temperature dependence (C_{m}∼T^{0.74}). On the contrary, we do not observe any significant contribution of thermal conductivity from magnetic excitations. In magnetic fields H≥6  T, the exponential T dependence of C_{m} and the enhanced thermal conductivity indicate a magnon gap of the fully polarized state...
December 23, 2016: Physical Review Letters
Rachel Barken
Within a neoliberal policy context that shifts responsibility for health and well-being from the state to families and individuals, Canadian home care strategies tend to present family members as "partners in care". Drawing on an interpretive grounded theory study that involved 34 qualitative interviews, this article examines older people's experiences at the intersections of formal home care and family/friend care arrangements, against the backdrop of policies that emphasize partnerships with family. The core concept derived from the interviews was reconciling tensions between care needs and concerns about burdening others, in the context of available home and community care...
January 5, 2017: Canadian Journal on Aging, la Revue Canadienne du Vieillissement
Felipe A Veloso
Changes in gene expression are thought to regulate the cell differentiation process intrinsically through complex epigenetic mechanisms. In fundamental terms, however, this assumed regulation refers only to the intricate propagation of changes in gene expression or else leads to non-explanatory regresses. The developmental self-regulatory dynamics and evolution of individuated multicellular organisms also lack a unified and falsifiable description. To fill this gap, I computationally analyzed publicly available high-throughput data of histone H3 post-translational modifications and mRNA abundance for different Homo sapiens, Mus musculus, and Drosophila melanogaster cell-type/developmental-period samples...
December 31, 2016: Journal of Theoretical Biology
Tess Nahanni Grainger, Rachel M Germain, Natalie T Jones, Benjamin Gilbert
Theory describing the positive effects of patch size and connectivity on diversity in fragmented systems has stimulated a large body of empirical work, yet predicting when and how local species interactions mediate these responses remains challenging. We used insects that specialize on milkweed plants as a model metacommunity to investigate how local predation alters the effects of biogeographic constraints on species distributions. Species-specific dispersal ability and susceptibility to predation were used to predict when patch size and connectivity should shape species distributions, and when these should be modified by local predator densities...
December 30, 2016: Ecology
David R Jacobson, Omar A Saleh
Nucleic acids are strongly negatively charged, and thus electrostatic interactions-screened by ions in solution-play an important role in governing their ability to fold and participate in biomolecular interactions. The negative charge creates a region, known as the ion atmosphere, in which cation and anion concentrations are perturbed from their bulk values. Ion counting experiments quantify the ion atmosphere by measuring the preferential ion interaction coefficient: the net total number of excess ions above, or below, the number expected due to the bulk concentration...
December 29, 2016: Nucleic Acids Research
Marta Favali, Giovanna Citti, Alessandro Sarti
This letter presents a mathematical model of figure-ground articulation that takes into account both local and global gestalt laws and is compatible with the functional architecture of the primary visual cortex (V1). The local gestalt law of good continuation is described by means of suitable connectivity kernels that are derived from Lie group theory and quantitatively compared with long-range connectivity in V1. Global gestalt constraints are then introduced in terms of spectral analysis of a connectivity matrix derived from these kernels...
February 2017: Neural Computation
Ian Donovan, Jay Pratt, Sarah Shomstein
Attentional selection is a dynamic process that relies on multiple types of representations. That object representations contribute to attentional selection has been known for decades; however, most evidence for this contribution has been gleaned from studies that have relied on various forms of spatial cueing (some endogenous and some exogenous). It has thus remained unclear whether object-based attentional selection is a direct result of spatial cuing, or whether it still emerges without any spatial marker...
December 27, 2016: Attention, Perception & Psychophysics
Walter Fierz
The immune system can be looked at as a cognitive system. This is often done in analogy to the neuro-psychological system. Here, it is demonstrated that the cognitive functions of the immune system can be properly described within a new theory of cognitive science. Gärdenfors' geometrical framework of conceptual spaces is applied to immune cognition. Basic notions, like quality dimensions, natural properties and concepts, similarities, prototypes, saliences, etc., are related to cognitive phenomena of the immune system...
2016: Frontiers in Immunology
A Bourgoin, A Hees, S Bouquillon, C Le Poncin-Lafitte, G Francou, M-C Angonin
Lorentz symmetry violations can be parametrized by an effective field theory framework that contains both general relativity and the standard model of particle physics called the standard-model extension (SME). We present new constraints on pure gravity SME coefficients obtained by analyzing lunar laser ranging (LLR) observations. We use a new numerical lunar ephemeris computed in the SME framework and we perform a LLR data analysis using a set of 20 721 normal points covering the period of August, 1969 to December, 2013...
December 9, 2016: Physical Review Letters
Simon Caron-Huot, Lance J Dixon, Andrew McLeod, Matt von Hippel
The analytic structure of scattering amplitudes is restricted by Steinmann relations, which enforce the vanishing of certain discontinuities of discontinuities. We show that these relations dramatically simplify the function space for the hexagon function bootstrap in planar maximally supersymmetric Yang-Mills theory. Armed with this simplification, along with the constraints of dual conformal symmetry and Regge exponentiation, we obtain the complete five-loop six-particle amplitude.
December 9, 2016: Physical Review Letters
Masahiko Matsubara, Rolando Saniz, Bart Partoens, Dirk Lamoen
We investigate the role of transition metal atoms of group V-b (V, Nb, and Ta) and VI-b (Cr, Mo, and W) as n- or p-type dopants in anatase TiO2 using thermodynamic principles and density functional theory with the Heyd-Scuseria-Ernzerhof HSE06 hybrid functional. The HSE06 functional provides a realistic value for the band gap, which ensures a correct classification of dopants as shallow or deep donors or acceptors. Defect formation energies and thermodynamic transition levels are calculated taking into account the constraints imposed by the stability of TiO2 and the solubility limit of the impurities...
January 18, 2017: Physical Chemistry Chemical Physics: PCCP
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