892 research outputs found

### Determining Structurally Identifiable Parameter Combinations Using Subset Profiling

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

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. Effectivenessâhow an intervention performs based on actual useâas opposed to efficacy will therefore be central to evaluations of new and existing interventions. Incomplete complianceâwhen people do not always use the intervention and are therefore exposed to contaminationâis thought to be responsible for the lowerâthanâexpected 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

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

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 TGFÎ˛ Receptor and Functions as an Antagonist of TGFÎ˛ Signaling

AbstractTGFÎ˛ 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 TGFÎ˛ signaling. Smad7 prevents TGFÎ˛-dependent formation of Smad2/Smad4 complexes and inhibits the nuclear accumulation of Smad2. Smad7 interacts stably with the activated TGFÎ˛ 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 TGFÎ˛ family receptors

### On the Two q-Analogue Logarithmic Functions

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

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 $(I=J=3/2 , 5/2 , \cdots ,
N_c/2 )$ in a manner fixed by large-$N_c$ 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 $\Delta$
decay width within a few MeV of its measured value, and furthermore, the
higher-spin baryons $(I=J \ge 5/2 )$ with widths so large ($\Gamma > 800 MeV$)
that these undesirable large-$N_c$ 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
$1/N_c$ 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

Recommended from our members

### Membrane-To-Nucleus Signaling Links Insulin-Like Growth Factor-1- and Stem Cell Factor-Activated Pathways

Stem cell factor (mouse: Kitl, human: KITLG) and insulin-like growth factor-1 (IGF1), acting via KIT and IGF1 receptor (IGF1R), respectively, are critical for the development and integrity of several tissues. Autocrine/paracrine KITLG-KIT and IGF1-IGF1R signaling are also activated in several cancers including gastrointestinal stromal tumors (GIST), the most common sarcoma. In murine gastric muscles, IGF1 promotes Kitl-dependent development of interstitial cells of Cajal (ICC), the non-neoplastic counterpart of GIST, suggesting cooperation between these pathways. Here, we report a novel mechanism linking IGF1-IGF1R and KITLG-KIT signaling in both normal and neoplastic cells. In murine gastric muscles, the microenvironment for ICC and GIST, human hepatic stellate cells (LX-2), a model for cancer niches, and GIST cells, IGF1 stimulated Kitl/KITLG protein and mRNA expression and promoter activity by activating several signaling pathways including AKT-mediated glycogen synthase kinase-3Î˛ inhibition (GSK3i). GSK3i alone also stimulated Kitl/KITLG expression without activating mitogenic pathways. Both IGF1 and GSK3i induced chromatin-level changes favoring transcriptional activation at the Kitl promoter including increased histone H3/H4 acetylation and H3 lysine (K) 4 methylation, reduced H3K9 and H3K27 methylation and reduced occupancy by the H3K27 methyltransferase EZH2. By pharmacological or RNA interference-mediated inhibition of chromatin modifiers we demonstrated that these changes have the predicted impact on KITLG expression. KITLG knock-down and immunoneutralization inhibited the proliferation of GIST cells expressing wild-type KIT, signifying oncogenic autocrine/paracrine KITLG-KIT signaling. We conclude that membrane-to-nucleus signaling involving GSK3i establishes a previously unrecognized link between the IGF1-IGF1R and KITLG-KIT pathways, which is active in both physiologic and oncogenic contexts and can be exploited for therapeutic purposes

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

The decays of $B$ 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

- âŚ