2,104 research outputs found
Turnpike Property and Convergence Rate for an Investment Model with General Utility Functions
In this paper we aim to address two questions faced by a long-term investor
with a power-type utility at high levels of wealth: one is whether the turnpike
property still holds for a general utility that is not necessarily
differentiable or strictly concave, the other is whether the error and the
convergence rate of the turnpike property can be estimated. We give positive
answers to both questions. To achieve these results, we first show that there
is a classical solution to the HJB equation and give a representation of the
solution in terms of the dual function of the solution to the dual HJB
equation. We demonstrate the usefulness of that representation with some
nontrivial examples that would be difficult to solve with the trial and error
method. We then combine the dual method and the partial differential equation
method to give a direct proof to the turnpike property and to estimate the
error and the convergence rate of the optimal policy when the utility function
is continuously differentiable and strictly concave. We finally relax the
conditions of the utility function and provide some sufficient conditions that
guarantee the turnpike property and the convergence rate in terms of both
primal and dual utility functions.Comment: 29 page
Design and Functional Assembly of Synthetic Biological Parts and Devices
Programming living cells with synthetic gene circuits to perform desired tasks has
been a major theme in the emerging field of synthetic biology. However, gene circuit
engineering currently lacks the same predictability and reliability as seen in other
mature engineering disciplines. This thesis focuses on the design and engineering of
novel modular and orthogonal biological devices, and the predictable functional
assembly of modular biological elements (BioParts) into customisable larger
biological devices.
The thesis introduces the design methodology for engineering modular and
orthogonal biological devices. A set of modular biological devices with digital logic
functions, including the AND, NOT and combinatorial NAND gates, were
constructed and quantitatively characterised. In particular, a novel genetic AND gate
was engineered in Escherichia coli by redesigning the natural HrpR/HrpS heteroregulation
motif in the hrp system of Pseudomonas syringae. The AND gate is
orthogonal to E. coli chassis, and employs the alternative Ï54-dependent gene
transcription to achieve tight transcriptional control. Results obtained show that
context has a large impact on part and device behaviour, established through the
systematic characterisation of a series of biological parts and devices in various
biophysical and genetic contexts. A new, effective strategy is presented for the
assembly of BioParts into functional customised systems using engineered âincontextâ
characterised modules aided by modelling, which can significantly increase
the predictability of circuit construction by characterising the component parts and
modules in the same biophysical and genetic contexts as anticipated in their final
systems. Finally, the thesis presents the design and construction of an application-oriented
integrated system â the cell density-dependent microbe-based biosensor. The
in vivo biosensor was programmed to be able to integrate its own cell density signal
through an engineered cell-cell communication module and a second environmental
signal through an environment-responsive promoter in the logic AND manner, with
GFP as the output readout
Smooth Value Functions for a Class of Nonsmooth Utility Maximization Problems
In this paper we prove that there exists a smooth classical solution to the
HJB equation for a large class of constrained problems with utility functions
that are not necessarily differentiable or strictly concave. The value function
is smooth if admissible controls satisfy an integrability condition or if it is
continuous on the closure of its domain. The key idea is to work on the dual
control problem and the dual HJB equation. We construct a smooth, strictly
convex solution to the dual HJB equation and show that its conjugate function
is a smooth, strictly concave solution to the primal HJB equation satisfying
the terminal and boundary conditions.Comment: 18 page
Generalized Yule-Walker Estimation for Spatio-Temporal Models with Unknown Diagonal Coefficients
We consider a class of spatio-temporal models which extend popular
econometric spatial autoregressive panel data models by allowing the scalar
coefficients for each location (or panel) different from each other. To
overcome the innate endogeneity, we propose a generalized Yule-Walker
estimation method which applies the least squares estimation to a Yule-Walker
equation. The asymptotic theory is developed under the setting that both the
sample size and the number of locations (or panels) tend to infinity under a
general setting for stationary and alpha-mixing processes, which includes
spatial autoregressive panel data models driven by i.i.d. innovations as
special cases. The proposed methods are illustrated using both simulated and
real data
Software defect prediction based on association rule classification.
In software defect prediction, predictive models are estimated based on various code attributes to assess the likelihood of software modules containing errors. Many classification methods have been suggested to accomplish this task. However, association based classification methods have not been investigated so far in this context. This paper assesses the use of such a classification method, CBA2, and compares it to other rule based classification methods. Furthermore, we investigate whether rule sets generated on data from one software project can be used to predict defective software modules in other, similar software projects. It is found that applying the CBA2 algorithm results in both accurate and comprehensible rule sets.Software defect prediction; Association rule classification; CBA2; AUC;
Rice microtubuleâassociated protein IQ67âDOMAIN14 regulates rice grain shape by modulating microtubule cytoskeleton dynamics
Cortical microtubule (MT) arrays play a critical role in plant cell shape determination by defining the direction of cell expansion. As plants continuously adapt to everâchanging environmental conditions, multiple environmental and developmental inputs need to be translated into changes of the MT cytoskeleton. Here, we identify and functionally characterize an auxinâinducible and MTâlocalized protein OsIQ67âDOMAIN14 (OsIQD14), which is highly expressed in rice seed hull cells. We show that while deficiency of OsIQD14 results in short and wide seeds and increases overall yield, overexpression leads to narrow and long seeds, caused by changed MT alignment. We further show that OsIQD14âmediated MT reordering is regulated by specifically affecting MT dynamics, and ectopic expression of OsIQD14 in Arabidopsis could change the cell shape both in pavement cells and hypocotyl cells. Additionally, OsIQD14 activity is tightly controlled by calmodulin proteins, providing an alternative way to modify the OsIQD14 activity. Our results indicate that OsIQD14 acts as a key factor in regulating MT rearrangements in rice hull cells and hence the grain shape, and allows effective local cell shape manipulation to improve the rice yield trait
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