892 research outputs found

    Determining Structurally Identifiable Parameter Combinations Using Subset Profiling

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    Identifiability is a necessary condition for successful parameter estimation of dynamic system models. A major component of identifiability analysis is determining the identifiable parameter combinations, the functional forms for the dependencies between unidentifiable parameters. Identifiable combinations can help in model reparameterization and also in determining which parameters may be experimentally measured to recover model identifiability. Several numerical approaches to determining identifiability of differential equation models have been developed, however the question of determining identifiable combinations remains incompletely addressed. In this paper, we present a new approach which uses parameter subset selection methods based on the Fisher Information Matrix, together with the profile likelihood, to effectively estimate identifiable combinations. We demonstrate this approach on several example models in pharmacokinetics, cellular biology, and physiology

    Linking Decision Theory and Quantitative Microbial Risk Assessment: Tradeoffs Between Compliance and Efficacy for Waterborne Disease Interventions

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    Achieving health gains from the U.N. Sustainable Development Goals of universal coverage for water and sanitation will require interventions that can be widely adopted and maintained. Effectiveness—how an intervention performs based on actual use—as opposed to efficacy will therefore be central to evaluations of new and existing interventions. Incomplete compliance—when people do not always use the intervention and are therefore exposed to contamination—is thought to be responsible for the lower‐than‐expected risk reductions observed from water, sanitation, and hygiene interventions based on their efficacy at removing pathogens. We explicitly incorporated decision theory into a quantitative microbial risk assessment model. Specifically, we assume that the usability of household water treatment (HWT) devices (filters and chlorine) decreases as they become more efficacious due to issues such as taste or flow rates. Simulations were run to examine the tradeoff between device efficacy and usability. For most situations, HWT interventions that trade lower efficacy (i.e., remove less pathogens) for higher compliance (i.e., better usability) contribute substantial reductions in diarrheal disease risk compared to devices meeting current World Health Organization efficacy guidelines. Recommendations that take into account both the behavioral and microbiological properties of treatment devices are likely to be more effective at reducing the burden of diarrheal disease than current standards that only consider efficacy.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151809/1/risa13381.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151809/2/risa13381-sup-0001-Appendix.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151809/3/risa13381_am.pd

    Pion-Nucleon Scattering in a Large-N Sigma Model

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    We review the large-N_c approach to meson-baryon scattering, including recent interesting developments. We then study pion-nucleon scattering in a particular variant of the linear sigma-model, in which the couplings of the sigma and pi mesons to the nucleon are echoed by couplings to the entire tower of I=J baryons (including the Delta) as dictated by large-N_c group theory. We sum the complete set of multi-loop meson-exchange \pi N --> \pi N and \pi N --> \sigma N Feynman diagrams, to leading order in 1/N_c. The key idea, reviewed in detail, is that large-N_c allows the approximation of LOOP graphs by TREE graphs, so long as the loops contain at least one baryon leg; trees, in turn, can be summed by solving classical equations of motion. We exhibit the resulting partial-wave S-matrix and the rich nucleon and Delta resonance spectrum of this simple model, comparing not only to experiment but also to pion-nucleon scattering in the Skyrme model. The moral is that much of the detailed structure of the meson-baryon S-matrix which hitherto has been uncovered only with skyrmion methods, can also be described by models with explicit baryon fields, thanks to the 1/N_c expansion.Comment: This LaTeX file inputs the ReVTeX macropackage; figures accompany i

    Optical Structure and Proper-Motion Age of the Oxygen-rich Supernova Remnant 1E 0102-7219 in the Small Magellanic Cloud

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    We present new optical emission-line images of the young SNR 1E 0102-7219 (E0102) in the SMC obtained with the HST Advanced Camera for Surveys (ACS). E0102 is a member of the oxygen-rich class of SNRs showing strong oxygen, neon , and other metal-line emissions in its optical and X-ray spectra, and an absence of H and He. The progenitor of E0102 may have been a Wolf-Rayet star that underwent considerable mass loss prior to exploding as a Type Ib/c or IIL/b SN. The ejecta in this SNR are fast-moving (V > 1000 km/s) and emit as they are compressed and heated in the reverse shock. In 2003, we obtained optical [O III], H-alpha, and continuum images with the ACS Wide Field Camera. The [O III] image captures the full velocity range of the ejecta, and shows considerable high-velocity emission projected in the middle of the SNR that was Doppler-shifted out of the narrow F502N bandpass of a previous Wide Field and Planetary Camera 2 image from 1995. Using these two epochs separated by ~8.5 years, we measure the transverse expansion of the ejecta around the outer rim in this SNR for the first time at visible wavelengths. From proper-motion measurements of 12 ejecta filaments, we estimate a mean expansion velocity for the bright ejecta of ~2000 km/s and an inferred kinematic age for the SNR of \~2050 +/- 600 years. The age we derive from HST data is about twice that inferred by Hughes et al.(2000) from X-ray data, though our 1-sigma error bars overlap. Our proper-motion age is consistent with an independent optical kinematic age derived by Eriksen et al.(2003) using spatially resolved [O III] radial-velocity data. We derive an expansion center that lies very close to X-ray and radio hotspots, which could indicate the presence of a compact remnant (neutron star or black hole).Comment: 28 pages, 8 figures. Accepted to the Astrophysical Journal, to appear in 20 April 2006 issue. Full resolution figures are posted at: http://stevenf.asu.edu/figure

    The MAD-Related Protein Smad7 Associates with the TGFβ Receptor and Functions as an Antagonist of TGFβ Signaling

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    AbstractTGFβ signaling is initiated when the type I receptor phosphorylates the MAD-related protein, Smad2, on C-terminal serine residues. This leads to Smad2 association with Smad4, translocation to the nucleus, and regulation of transcriptional responses. Here we demonstrate that Smad7 is an inhibitor of TGFβ signaling. Smad7 prevents TGFβ-dependent formation of Smad2/Smad4 complexes and inhibits the nuclear accumulation of Smad2. Smad7 interacts stably with the activated TGFβ type I receptor, thereby blocking the association, phosphorylation, and activation of Smad2. Furthermore, mutations in Smad7 that interfere with receptor binding disrupt its inhibitory activity. These studies thus define a novel function for MAD-related proteins as intracellular antagonists of the type I kinase domain of TGFβ family receptors

    On the Two q-Analogue Logarithmic Functions

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    There is a simple, multi-sheet Riemann surface associated with e_q(z)'s inverse function ln_q(w) for 0< q < 1. A principal sheet for ln_q(w) can be defined. However, the topology of the Riemann surface for ln_q(w) changes each time "q" increases above the collision point of a pair of the turning points of e_q(x). There is also a power series representation for ln_q(1+w). An infinite-product representation for e_q(z) is used to obtain the ordinary natural logarithm ln{e_q(z)} and the values of sum rules for the zeros "z_i" of e_q(z). For |z|<|z_1|, e_q(z)=exp{b(z)} where b(z) is a simple, explicit power series in terms of values of these sum rules. The values of the sum rules for the q-trigonometric functions, sin_q(z) and cos_q(z), are q-deformations of the usual Bernoulli numbers.Comment: This is the final version to appear in J.Phys.A: Math. & General. Some explict formulas added, and to update the reference

    Skyrmion Quantization and the Decay of the Delta

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    We present the complete solution to the so-called ``Yukawa problem'' of the Skyrme model. This refers to the perceived difficulty of reproducing---purely from soliton physics---the usual pseudovector pion-nucleon coupling, echoed by pion coupling to the higher spin/isospin baryons (I=J=3/2,5/2,,Nc/2)(I=J=3/2 , 5/2 , \cdots , N_c/2 ) in a manner fixed by large-NcN_c group theory. The solution involves surprisingly elegant interplay between the classical and quantum properties of a new configuration, the ``new improved skyrmion''. This is the near-hedgehog obtained by minimizing the usual skyrmion mass functional augmented by an all-important isorotational kinetic term. The numerics are pleasing: a Δ\Delta decay width within a few MeV of its measured value, and furthermore, the higher-spin baryons (I=J5/2)(I=J \ge 5/2 ) with widths so large (Γ>800MeV\Gamma > 800 MeV) that these undesirable large-NcN_c artifacts effectively drop out of the spectrum, and pose no phenomenological problem. Beyond these specific results, we ground the Skyrme model in the Feynman Path Integral, and set up a transparent collective coordinate formalism that makes maximal use of the 1/Nc1/N_c expansion. This approach elucidates the connection between skyrmions on the one hand, and Feynman diagrams in an effective field theory on the other.Comment: This TeX file inputs the macropackage harvmac.tex . Choose the ``b'' (big) option or equations will overrun

    Broken SU(3) Symmetry in Two-Body B Decays

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    The decays of BB mesons to two-body hadronic final states are analyzed within the context of broken flavor SU(3) symmetry, extending a previous analysis involving pairs of light pseudoscalars to decays involving one or two charmed quarks in the final state. A systematic program is described for learning information {}from decay rates regarding (i) SU(3)-violating contributions, (ii) the magnitude of exchange and annihilation diagrams (effects involving the spectator quark), and (iii) strong final-state interactions. The implication of SU(3)-breaking effects for the extraction of weak phases is also examined. The present status of data on these questions is reviewed and suggestions for further experimental study are made.Comment: 38 pages, 8 figures, LaTeX file. The full postscript manuscript is available by anon ftp at ftp://lpsvsh.lps.umontreal.ca/theorie/hep-ph/SU3break.ps (a VAX so use the format theorie.hep-ph if you change by more than one directory at a time