2,404 research outputs found
Nonlinear Model Predictive Control for Constrained Output Path Following
We consider the tracking of geometric paths in output spaces of nonlinear
systems subject to input and state constraints without pre-specified timing
requirements. Such problems are commonly referred to as constrained output
path-following problems. Specifically, we propose a predictive control approach
to constrained path-following problems with and without velocity assignments
and provide sufficient convergence conditions based on terminal regions and end
penalties. Furthermore, we analyze the geometric nature of constrained output
path-following problems and thereby provide insight into the computation of
suitable terminal control laws and terminal regions. We draw upon an example
from robotics to illustrate our findings.Comment: 12 pages, 4 figure
Education and Optimal Dynamic Taxation
We study optimal tax and educational policies in a dynamic private information economy, in which ex-ante heterogeneous individuals make an educational investment early in their life and face a stochastic wage distribution. We characterize labor and education wedges in this setting analytically and numerically, using a calibrated example. We present ways to implement the optimum. In one implementation there is a common labor income tax schedule, and a repayment schedule for government loans given out to agents during education. These repayment plans are contingent on loan size and income and capture the history dependence of the labor wedges. Applying the model to US-data and a binary education decision (graduating from college or not) we characterize optimal labor wedges for individuals without college degree and with college degree. The labor wedge of college graduates as a function of income lies first strictly above their counterparts from high-school, but this reverses at higher incomes. The loan repayment schedule is hump-shaped in income for college graduates.optimal dynamic taxation, education, implementation
A Simple Calculation in Service of Constraining the Rate of FU Orionis Outburst Events from Photometric Monitoring Surveys
An enigmatic and rare type of young stellar object is the FU Orionis class.
The members are interpreted as "outbursting," that is, currently in a state of
enhanced accretion by several orders of magnitude relative to the more modest
disk-to-star accretion rates measured in typical T Tauri stars. They are key to
our understanding of the history of stellar mass assembly and pre-main sequence
evolution, as well as critical to consider in the chemical and physical
evolution of the circumstellar environment -- where planets form. A common
supposition is that *all* T Tauri stars undergo repeated such outbursts, more
frequently in their earlier evolutionary stages when the disks are more
massive, so as to build up the requisite amount of stellar mass on the required
time scale. However, the actual data supporting this traditional picture of
episodically enhanced disk accretion are limited, and the observational
properties of the known sample of FU Ori objects quite diverse. To improve our
understanding of these rare objects, we outline the logic for meaningfully
constraining the rate of FU Ori outbursts and present numbers to guide
parameter choices in the analysis of time domain surveys.Comment: accepted for publication in Ap
Education and optimal dynamic taxation: The role of income-contingent student loans
We study Pareto optimal tax and education policies when human capital upon labor market entry is endogenous and individuals face wage uncertainty. Though optimal labor distortions are history-dependent, i.e. depend on income and education, simple policy instruments can yield the desired distortions: a single nonlinear labor income tax schedule combined with income-contingent loans. To take themodel to the (US) data, we simplify the model to a binary education decision (graduating from college or not). We find that for lowand intermediate incomes the labor supply decision of college graduates should be distorted more heavily than for individuals without a college degree. As a consequence, the optimal student loan repayment schedule increases in income for this range. This result holds along the Pareto frontier. We compare the second best to a situation where loan repayment is restricted to be independent from income and find significant welfare gains.Optimal dynamic taxation, education, implementation
Implementation of Nonlinear Model Predictive Path-Following Control for an Industrial Robot
Many robotic applications, such as milling, gluing, or high precision
measurements, require the exact following of a pre-defined geometric path. In
this paper, we investigate the real-time feasible implementation of model
predictive path-following control for an industrial robot. We consider
constrained output path following with and without reference speed assignment.
We present results from an implementation of the proposed model predictive
path-following controller on a KUKA LWR IV robot.Comment: 8 pages, 3 figures; final revised versio
On output feedback nonlinear model predictive control using high gain observers for a class of systems
In recent years, nonlinear model predictive control schemes have been derived that guarantee stability of the closed loop under the assumption of full state information. However, only limited advances have been made with respect to output feedback in connection to nonlinear predictive control. Most of the existing approaches for output feedback nonlinear model predictive control do only guarantee local stability. Here we consider the combination of stabilizing instantaneous NMPC schemes with high gain observers. For a special MIMO system class we show that the closed loop is asymptotically stable, and that the output feedback NMPC scheme recovers the performance of the state feedback in the sense that the region of attraction and the trajectories of the state feedback scheme are recovered for a high gain observer with large enough gain and thus leading to semi-global/non-local results
Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse
The search for binarity in AGB stars is of critical importance for our
understanding of how planetary nebulae acquire the dazzling variety of
aspherical shapes which characterises this class. However, detecting binary
companions in such stars has been severely hampered due to their extreme
luminosities and pulsations. We have carried out a small imaging survey of AGB
stars in ultraviolet light (using GALEX) where these cool objects are very
faint, in order to search for hotter companions. We report the discovery of
significant far-ultraviolet excesses towards nine of these stars. The
far-ultraviolet excess most likely results either directly from the presence of
a hot binary companion, or indirectly from a hot accretion disk around the
companion.Comment: revised for Astrophysical Journa
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