2,922 research outputs found
Likelihood based observability analysis and confidence intervals for predictions of dynamic models
Mechanistic dynamic models of biochemical networks such as Ordinary
Differential Equations (ODEs) contain unknown parameters like the reaction rate
constants and the initial concentrations of the compounds. The large number of
parameters as well as their nonlinear impact on the model responses hamper the
determination of confidence regions for parameter estimates. At the same time,
classical approaches translating the uncertainty of the parameters into
confidence intervals for model predictions are hardly feasible.
In this article it is shown that a so-called prediction profile likelihood
yields reliable confidence intervals for model predictions, despite arbitrarily
complex and high-dimensional shapes of the confidence regions for the estimated
parameters. Prediction confidence intervals of the dynamic states allow a
data-based observability analysis. The approach renders the issue of sampling a
high-dimensional parameter space into evaluating one-dimensional prediction
spaces. The method is also applicable if there are non-identifiable parameters
yielding to some insufficiently specified model predictions that can be
interpreted as non-observability. Moreover, a validation profile likelihood is
introduced that should be applied when noisy validation experiments are to be
interpreted.
The properties and applicability of the prediction and validation profile
likelihood approaches are demonstrated by two examples, a small and instructive
ODE model describing two consecutive reactions, and a realistic ODE model for
the MAP kinase signal transduction pathway. The presented general approach
constitutes a concept for observability analysis and for generating reliable
confidence intervals of model predictions, not only, but especially suitable
for mathematical models of biological systems
Potential of the next generation VHE instruments to probe the EBL (I): the low- and mid-VHE
The diffuse meta-galactic radiation field at ultraviolet to infrared
wavelengths - commonly labeled extragalactic background light (EBL) - contains
the integrated emission history of the universe. Difficult to access via direct
observations indirect constraints on its density can be derived through
observations of very-high energy (VHE; E>100 GeV) gamma-rays from distant
sources: the VHE photons are attenuated via pair-production with the low energy
photons from the EBL, leaving a distinct imprint in the VHE spectra measured on
earth. Discoveries made with current generation VHE observatories like H.E.S.S.
and MAGIC enabled strong constraints on the density of the EBL especially in
the near-infrared. In this article the prospect of future VHE observatories to
derive new constraints on the EBL density are discussed. To this end, results
from current generation instruments will be extrapolated to the future
experiment's sensitivity and investigated for their power to enable new methods
and improved constraints on the EBL density.Comment: Accepted for publication in Astroparticle Physics; v2: extended
discussion following referees comments, conclusions unchange
Optical depth for VHE gamma-rays from distant sources from a generic EBL density
Very-high-energy (VHE; E>100GeV) gamma-rays from distant sources suffer
attenuation through pair-production with low energy photons from the diffuse
extragalactic photon fields in the ultraviolet (UV) to far-infrared (FIR)
(commonly referred to as Extragalactic Background Light; EBL). When modeling
the intrinsic spectra of the VHE gamma-ray sources it is crucial to correctly
account for the attenuation. Unfortunately, direct measurements of the EBL are
difficult and the knowledge about the EBL over certain wavelength ranges is
poor. To calculate the EBL attenuation usually predictions from theoretical
models are used. Recently, the limits on the EBL from direct and indirect
methods have narrowed down the possible EBL range and many of the previous
models are in conflict with these limits. We propose a new generic EBL density
(not a complete model), which is in compliance with the new EBL limits. EBL
evolution with redshift is included in the calculation in a very simple but
effective ad-hoc way. Properties of this generic EBL are discussed.Comment: Proceedings of the workshop 'High Energy Phenomena in Relativistic
Outflows' (HEPRO), Dublin, 24-28 September 200
Genotype-phenotype correlation in multiple endocrine neoplasia type 2
Multiple endocrine neoplasia type 2 is an autosomal-dominant hereditary cancer syndrome caused by missense gain-of-function mutations of the rearranged during transfection proto-oncogene, which encodes the receptor tyrosine kinase, on chromosome 10. It has a strong penetrance of medullary thyroid carcinomas and can be associated with bilateral pheochromocytoma and primary hyperparathyroidism. Multiple endocrine neoplasia type 2 is divided into three varieties depending on its clinical features: multiple endocrine neoplasia type 2A, multiple endocrine neoplasia type 2B, and familial medullary thyroid carcinoma. The specific rearranged during transfection mutation may suggest a predilection toward a particular phenotype and clinical course of medullary thyroid carcinoma, with strong genotype-phenotype correlations. Offering rearranged during transfection testing is the best practice for the clinical management of patients at risk of developing multiple endocrine neoplasia type 2, and multiple endocrine neoplasia type 2 has become a classic model for the integration of molecular medicine into patient care. Recommendations on the timing of prophylactic thyroidectomy and extent of surgery are based on the classification of rearranged during transfection mutations into risk levels according to genotype-phenotype correlations. Earlier identification of patients with hereditary medullary thyroid carcinoma can change the presentation from clinical tumor to preclinical disease, resulting in a high cure rate of affected patients and a much better prognoses
Electroproduction of (1405)
The electroproduction of (1405) was studied by analyzing the
E1F data set collected in Hall B at Jefferson Lab. The analysis utilized the
decay channel of the (1405) and of the
. Simulations of background, (1405) and (1520)
production according to PDG values were performed by using standard CLAS
analysis tools adapted for the E1F run. Fits of the acceptance-corrected
simulations were made to the acceptance-corrected data to determine
contributions from signal and background processes. The line shape of
(1405) varies with the four momentum transfer, , and does not match the
line shape based on PDG resonance parameters. It corresponds approximately to
predictions of a recent two-pole meson-baryon picture of this state.Comment: 4 pages, 6 figures, Contribution to the Proceedings of "NSTAR2011 -
The 8th International Workshop on the Physics of Excited Nucleons," Thomas
Jefferson National Accelerator Facility, Newport News, Virginia USA, 17-20
May 201
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