459 research outputs found
Approximately Optimal Controllers for Quantitative Two-Phase Reach-Avoid Problems on Nonlinear Systems
The present work deals with quantitative two-phase reach-avoid problems on
nonlinear control systems. This class of optimal control problem requires the
plant's state to visit two (rather than one) target sets in succession while
minimizing a prescribed cost functional. As we illustrate, the naive approach,
which subdivides the problem into the two evident classical reach-avoid tasks,
usually does not result in an optimal solution. In contrast, we prove that an
optimal controller is obtained by consecutively solving two special
quantitative reach-avoid problems. In addition, we present a fully-automated
method based on Symbolic Optimal Control to practically synthesize for the
considered problem class approximately optimal controllers for sampled-data
nonlinear plants. Experimental results on parcel delivery and on an aircraft
routing mission confirm the practicality of our method.Comment: 14 pages, 7 figure
Enhancing ordering dynamics in solvent-annealed block-copolymer films by lithographic hard masks supports
We studied solvent-driven ordering dynamics of block copolymer films
supported by a densely cross-linked polymer network designed as organic hard
mask (HM) for lithographic fabrications. The ordering of microphase separated
domains at low degrees of swelling corresponding to intermediate/strong
segregation regimes was found to proceed significantly faster in films on a HM
layer as compared to similar block copolymer films on silicon wafers. The
ten-fold enhancement of the chain mobility was evident in the dynamics of
morphological phase transitions and of related process of terrace-formation on
a macroscale, as well as in the degree of long-range lateral order of
nanostructures. The effect is independent of the chemical structure and on the
volume composition (cylinder-/ lamella-forming) of the block copolymers.
In-situ ellipsometric measurements of the swelling behavior revealed a
cumulative increase in 1-3 vol. % in solvent up-take by HM-block copolymer
bilayer films, so that we suggest other than dilution effect reasons for the
observed significant enhancement of the chain mobility in concentrated block
copolymer solutions. Another beneficial effect of the HM-support is the
suppression of the film dewetting which holds true even for low molecular
weight homopolymer polystyrene films at high degrees of swelling. Apart from
immediate technological impact in block copolymer-assisted nanolithography, our
findings convey novel insight into effects of molecular architecture on
polymer-solvent interactions.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Macromolecules, copyright
\c{opyright} American Chemical Society after peer review. To access the final
edited and published work see http://pubs.acs.org/doi/abs/10.1021/ma500561
FORFIS: A forest fire firefighting simulation tool for education and research
We present a forest fire firefighting simulation tool named FORFIS that is
implemented in Python. Unlike other existing software, we focus on a
user-friendly software interface with an easy-to-modify software engine. Our
tool is published under GNU GPLv3 license and comes with a GUI as well as
additional output functionality. The used wildfire model is based on the
well-established approach by cellular automata in two variants - a rectangular
and a hexagonal cell decomposition of the wildfire area. The model takes wind
into account. In addition, our tool allows the user to easily include a
customized firefighting strategy for the firefighting agents.Comment: 5 figure
Multi-scale space-variant FRep cellular structures
Existing mesh and voxel based modeling methods encounter difficulties when dealing with objects containing cellular structures
on several scale levels and varying their parameters in space. We describe an alternative approach based on using real functions evaluated procedurally at any given point. This allows for modeling fully parameterized, nested and multi-scale cellular
structures with dynamic variations in geometric and cellular properties. The geometry of a base unit cell is defined using Function Representation (FRep) based primitives and operations. The unit cell is then replicated in space using periodic
space mappings such as sawtooth and triangle waves. While being replicated, the unit cell can vary its geometry and topology due
to the use of dynamic parameterization. We illustrate this approach by several examples of microstructure generation within a given volume or
along a given surface. We also outline some methods for direct rendering and fabrication not involving auxiliary mesh and voxel
representations
Meta-Reinforcement Learning via Language Instructions
Although deep reinforcement learning has recently been very successful at
learning complex behaviors, it requires a tremendous amount of data to learn a
task. One of the fundamental reasons causing this limitation lies in the nature
of the trial-and-error learning paradigm of reinforcement learning, where the
agent communicates with the environment and progresses in the learning only
relying on the reward signal. This is implicit and rather insufficient to learn
a task well. On the contrary, humans are usually taught new skills via natural
language instructions. Utilizing language instructions for robotic motion
control to improve the adaptability is a recently emerged topic and
challenging. In this paper, we present a meta-RL algorithm that addresses the
challenge of learning skills with language instructions in multiple
manipulation tasks. On the one hand, our algorithm utilizes the language
instructions to shape its interpretation of the task, on the other hand, it
still learns to solve task in a trial-and-error process. We evaluate our
algorithm on the robotic manipulation benchmark (Meta-World) and it
significantly outperforms state-of-the-art methods in terms of training and
testing task success rates. Codes are available at
\url{https://tumi6robot.wixsite.com/million}
Topoisomerase 3α and RMI1 Suppress Somatic Crossovers and Are Essential for Resolution of Meiotic Recombination Intermediates in Arabidopsis thaliana
Topoisomerases are enzymes with crucial functions in DNA metabolism. They are ubiquitously present in prokaryotes and eukaryotes and modify the steady-state level of DNA supercoiling. Biochemical analyses indicate that Topoisomerase 3α (TOP3α) functions together with a RecQ DNA helicase and a third partner, RMI1/BLAP75, in the resolution step of homologous recombination in a process called Holliday Junction dissolution in eukaryotes. Apart from that, little is known about the role of TOP3α in higher eukaryotes, as knockout mutants show early lethality or strong developmental defects. Using a hypomorphic insertion mutant of Arabidopsis thaliana (top3α-2), which is viable but completely sterile, we were able to define three different functions of the protein in mitosis and meiosis. The top3α-2 line exhibits fragmented chromosomes during mitosis and sensitivity to camptothecin, suggesting an important role in chromosome segregation partly overlapping with that of type IB topoisomerases. Furthermore, AtTOP3α, together with AtRECQ4A and AtRMI1, is involved in the suppression of crossover recombination in somatic cells as well as DNA repair in both mammals and A. thaliana. Surprisingly, AtTOP3α is also essential for meiosis. The phenotype of chromosome fragmentation, bridges, and telophase I arrest can be suppressed by AtSPO11 and AtRAD51 mutations, indicating that the protein is required for the resolution of recombination intermediates. As Atrmi1 mutants have a similar meiotic phenotype to Attop3α mutants, both proteins seem to be involved in a mechanism safeguarding the entangling of homologous chromosomes during meiosis. The requirement of AtTOP3α and AtRMI1 in a late step of meiotic recombination strongly hints at the possibility that the dissolution of double Holliday Junctions via a hemicatenane intermediate is indeed an indispensable step of meiotic recombination
Enantioselektive Synthese von (1S,4R)-4-Hydroxycyclopent-2-enyl-acetat durch enzym-katalysierte Veresterung von cis-Cyclopent-2-en-1,4-diol mit Acetanhydrid. Gaschromatographische Untersuchungen zum Reaktionsmechanismus
(1S,4R)-4-Hydroxycyclopent-2-enyl-acetate (1), an attractive starting material for the synthesis of prostaglandins, was readily prepared by an enzyme-catalyzed interesterification procedure using acetic anhydride as acylation agent. As the chemical yield of the chiral monoacylation product is rather low (45%), we investigated the acylation mechanism of this reaction to optimize the product output. Kinetic measurements were carried out by means of gas chromatography on a chiral stationary phase, synthesized by methylation of β-cyclodextrin
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