1,953 research outputs found
The Future of Drug Development: The Economics of Pharmacogenomics
This paper models how the evolving field of pharmacogenomics (PG), which is the science of using genomic markers to predict drug response, may impact drug development times, attrition rates, costs, and the future returns to research and development (R&D). While there still remains an abundance of uncertainty around how PG will impact the future landscape of pharmaceutical and biological R&D, we identify several likely outcomes. We conclude PG has the potential to significantly reduce both expected drug development costs (via higher probabilities of technical success, shorter clinical development times, and smaller clinical trials) and returns. The impact PG has on expected returns is partially mitigated by higher equilibrium prices, expedited product launches, and longer effective patent lives. Our conclusions are, of course, accompanied by numerous caveats.
Use of Multivariate Techniques to Validate and Improved the Current USAF Pilot Candidate Selection Model
The Pilot Candidate Selection Method (PCSM) seeks to ensure the highest possible probability of success at UPT. PCSM applies regression weights to a candidate\u27s Air Force Officer Qualification Test (AFOQT) Pilot composite score, self-reported flying hours, and five Basic Attributes Test (BAT) score composites. PCSM scores range between 0 and 99 and is interpreted as a candidate\u27s probability of passing UPT. The goal of this study is to apply multivariate data analysis techniques to validate PCSM and determine appropriate changes to the model\u27s weights. Performance of the updated weights is compared to the current PCSM model via Receiver Operating Curves (ROC). In addition, two independent models are developed using multi-layer perceptron neural networks and discriminant analysis. Both linear and logistic regression is used to investigate possible updates to PCSM\u27s current linear regression weights. An independent test set is used to estimate the generalized performance of the regressions and independent models. Validation of the current PCSM model demonstrated in the first phase of this research is enhanced by the fact that PCSM outperforms all other models developed in the research
A normal form for excitable media
We present a normal form for travelling waves in one-dimensional excitable
media in form of a differential delay equation. The normal form is built around
the well-known saddle-node bifurcation generically present in excitable media.
Finite wavelength effects are captured by a delay. The normal form describes
the behaviour of single pulses in a periodic domain and also the richer
behaviour of wave trains. The normal form exhibits a symmetry preserving Hopf
bifurcation which may coalesce with the saddle-node in a Bogdanov-Takens point,
and a symmetry breaking spatially inhomogeneous pitchfork bifurcation. We
verify the existence of these bifurcations in numerical simulations. The
parameters of the normal form are determined and its predictions are tested
against numerical simulations of partial differential equation models of
excitable media with good agreement.Comment: 22 pages, accepted for publication in Chao
Instability and spatiotemporal rheochaos in a shear-thickening fluid model
We model a shear-thickening fluid that combines a tendency to form
inhomogeneous, shear-banded flows with a slow relaxational dynamics for fluid
microstructure. The interplay between these factors gives rich dynamics, with
periodic regimes (oscillating bands, travelling bands, and more complex
oscillations) and spatiotemporal rheochaos. These phenomena, arising from
constitutive nonlinearity not inertia, can occur even when the steady-state
flow curve is monotonic. Our model also shows rheochaos in a low-dimensional
truncation where sharply defined shear bands cannot form
Pulse propagation in discrete systems of coupled excitable cells
Propagation of pulses in myelinated fibers may be described by appropriate
solutions of spatially discrete FitzHugh-Nagumo systems. In these systems,
propagation failure may occur if either the coupling between nodes is not
strong enough or the recovery is too fast. We give an asymptotic construction
of pulses for spatially discrete FitzHugh-Nagumo systems which agrees well with
numerical simulations and discuss evolution of initial data into pulses and
pulse generation at a boundary. Formulas for the speed and length of pulses are
also obtained.Comment: 16 pages, 10 figures, to appear in SIAM J. Appl. Mat
Wave trains, self-oscillations and synchronization in discrete media
We study wave propagation in networks of coupled cells which can behave as
excitable or self-oscillatory media. For excitable media, an asymptotic
construction of wave trains is presented. This construction predicts their
shape and speed, as well as the critical coupling and the critical separation
of time scales for propagation failure. It describes stable wave train
generation by repeated firing at a boundary. In self-oscillatory media, wave
trains persist but synchronization phenomena arise. An equation describing the
evolution of the oscillator phases is derived.Comment: to appear in Physica D: Nonlinear Phenomen
Universal behavior in populations composed of excitable and self-oscillatory elements
We study the robustness of self-sustained oscillatory activity in a globally
coupled ensemble of excitable and oscillatory units. The critical balance to
achieve collective self-sustained oscillations is analytically established. We
also report a universal scaling function for the ensemble's mean frequency. Our
results extend the framework of the `Aging Transition' [Phys. Rev. Lett. 93,
104101 (2004)] including a broad class of dynamical systems potentially
relevant in biology.Comment: 4 pages; Changed titl
Spontaneous spiking in an autaptic Hodgkin-Huxley set up
The effect of intrinsic channel noise is investigated for the dynamic
response of a neuronal cell with a delayed feedback loop. The loop is based on
the so-called autapse phenomenon in which dendrites establish not only
connections to neighboring cells but as well to its own axon. The biophysical
modeling is achieved in terms of a stochastic Hodgkin-Huxley model containing
such a built in delayed feedback. The fluctuations stem from intrinsic channel
noise, being caused by the stochastic nature of the gating dynamics of ion
channels. The influence of the delayed stimulus is systematically analyzed with
respect to the coupling parameter and the delay time in terms of the interspike
interval histograms and the average interspike interval. The delayed feedback
manifests itself in the occurrence of bursting and a rich multimodal interspike
interval distribution, exhibiting a delay-induced reduction of the spontaneous
spiking activity at characteristic frequencies. Moreover, a specific
frequency-locking mechanism is detected for the mean interspike interval.Comment: 8 pages, 10 figure
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