5,401 research outputs found
Formation Navigation and Relative Localisation of Multi-Robot Systems
When proceeding from single to multiple robots, cooperative action is one of the most relevant topics. The domain of robotic security systems contains typical applications for a multi-robot system (MRS). Possible scenarios are safety and security issues on airports, harbours, large industry plants or museums. Additionally, the field of environmental supervision is an up-coming issue. Inherent to these applications is the need for an organised and coordinated navigation of the robots, and a vital prerequisite for any coordinated movements is a good localisation. This dissertation will present novel approaches to the problems of formation navigation and relative localisation with multiple ground-based mobile robots. It also looks into the question what kind of metric is applicable for multi-robot navigation problems. Thereby, the focus of this work will be on aspects of 1. coordinated navigation and movement A new potential-field-based approach to formation navigation is presented. In contradiction to classical potential-field-based formation approaches, the proposed method also uses the orientation between neighbours in the formation. Consequently, each robot has a designated position within the formation. Therefore, the new method is called directed potential field approach. Extensive experiments prove that the method is capable of generating all kinds of formation shapes, even in the presence of dense obstacles. All tests have been conducted with simulated and real robots and successfully guided the robot formation through environments with varying obstacle configurations. In comparison, the nondirected potential field approach turns out to be unstable regarding the positions of the robots within formations. The robots strive to switch their positions, e.g. when passing through narrow passages. Under such conditions the directed approach shows a preferable behaviour, called βbreathingβ. The formation shrinks or inflates depending on the obstacle situation while trying to maintain its shape and keep the robots at their desired positions inside the formation. For a more particular comparison of formation algorithms it is important to have measures that allow a meaningful evaluation of the experimental data. For this purpose a new formation metric is developed. If there are many obstacles, the formation error must be scaled down to be comparable to an empty environment where the error would be small. Assuming that the environment is unknown and possibly non-static, only actual sensor information can be used for these calculations. We developed a special weighting factor, which is inverse proportional to the βdensityβ of obstacles and which turns out to model the influence of the environment adequately. 2. relative localisation A new method for relative localisation between the members of a robot group is introduced. This relative localisation approach uses mutual sensor observations to localise the robots with respect to other objects β without having an environment model. Techniques like the Extended Kalman Filter (EKF) have proven to be powerful tools in the field of single robot applications. This work presents extensions to these algorithms with respect to the use in MRS. These aspects are investigated and combined under the topic of improving and stabilising the performance of the localisation and navigation process. Most of the common localisation approaches use maps and/or landmarks with the intention of generating a globally consistent world-coordinate system for the robot group. The aim of the here presented relative localisation approach, on the other hand, is to maintain only relative positioning between the robots. The presented method enables a group of mobile robots to start at an unknown location in an unknown environment and then to incrementally estimate their own positions and the relative locations of the other robots using only sensor information. The result is a robust, fast and precise approach, which does not need any preconditions or special assumptions about the environment. To validate the approach extensive tests with both, real and simulated, robots have been conducted. For a more specific evaluation, the Mean Localisation Error (MLE) is introduced. The conducted experiments include a comparison between the proposed Extended Kalman Filter and a standard SLAM-based approach. The developed method robustly delivered an accuracy better than 2 cm and performed at least as well as the SLAM approach. The algorithm coped with scattered groups of robots while moving on arbitrarily shaped paths. In summary, this thesis presents novel approaches to the field of coordinated navigation in multi-robot systems. The results facilitate cooperative movements of robot groups as well as relative localisation among the group members. In addition, a solid foundation for a non-environment related metric for formation navigation is introduced
Phase diagram of two-dimensional hard rods from fundamental mixed measure density functional theory
A density functional theory for the bulk phase diagram of two-dimensional orientable hard rods is proposed and tested against Monte Carlo computer simulation data. In detail, an explicit density functional is derived from fundamental mixed measure theory and freely minimized numerically for hard discorectangles. The phase diagram, which involves stable isotropic, nematic, smectic, and crystalline phases, is obtained and shows good agreement with the simulation data. Our functional is valid for a multicomponent mixture of hard particles with arbitrary convex shapes and provides a reliable starting point to explore various inhomogeneous situations of two-dimensional hard rods and their Brownian dynamics
ΠΠ°ΠΊΠΎΠ½ΠΎΠΌΠ΅ΡΠ½ΠΎΡΡΠΈ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΌΠ°ΠΊΡΠΈΠΌΠ°Π»ΡΠ½ΡΡ ΠΎΡΠ΅Π΄Π°Π½ΠΈΠΉ ΠΈ Π½Π°ΠΊΠ»ΠΎΠ½ΠΎΠ² Π·Π΅ΠΌΠ½ΠΎΠΉ ΠΏΠΎΠ²Π΅ΡΡ Π½ΠΎΡΡΠΈ Π½Π° ΡΡΠ°Π΄ΠΈΠΈ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΌΡΠ»ΡΠ΄Ρ ΡΠ΄Π²ΠΈΠΆΠ΅Π½ΠΈΡ
ΠΡΠΈΠ²Π΅Π΄Π΅Π½Ρ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠΉ ΠΌΡΠ»ΡΠ΄Ρ ΠΎΡΠ΅Π΄Π°Π½ΠΈΡ Π½Π° ΡΡΠ°Π΄ΠΈΠΈ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ. Π£ΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½Ρ Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΠΈ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΈΡ ΠΈ Π²Π΅Π»ΠΈΡΠΈΠ½ ΠΌΠ°ΠΊΡΠΈΠΌΠ°Π»ΡΠ½ΡΡ
ΠΎΡΠ΅Π΄Π°Π½ΠΈΠΉ ΠΈ Π½Π°ΠΊΠ»ΠΎΠ½ΠΈΠ² Π·Π΅ΠΌΠ½ΠΎΠΉ ΠΏΠΎΠ²Π΅ΡΡ
Π½ΠΎΡΡΠΈ ΠΎΡ ΠΏΠΎΠ΄Π²ΠΈΠ³Π°Π½ΠΈΡ ΠΎΡΠΈΡΡΠ½ΠΎΠ³ΠΎ Π·Π°Π±ΠΎΡ.The findings of investigation of a subsidence trough at a formation stage are explained. Dependences of position and value of maximum subsidence and tilt from the size of mined-out space are determined
Spin-Selective Electron Transport Through Single Chiral Molecules
The interplay between chirality and magnetism has been a source of
fascination among scientists for over a century. In recent years,
chirality-induced spin selectivity (CISS) has attracted renewed interest. It
has been observed that electron transport through layers of homochiral
molecules leads to a significant spin polarization of several tens of percent.
Despite the abundant experimental evidence gathered through mesoscopic
transport measurements, the exact mechanism behind CISS remains elusive. In
this study, we report spin-selective electron transport through single helical
aromatic hydrocarbons that were sublimed in vacuo onto ferromagnetic cobalt
surfaces and examined with spin-polarized scanning tunneling microscopy
(SP-STM) at a temperature of 5 K. Direct comparison of two enantiomers under
otherwise identical conditions revealed magnetochiral conductance asymmetries
of up to 50% when either the molecular handedness was exchanged or the
magnetization direction of the STM tip or Co substrate was reversed.
Importantly, our results rule out electron-phonon coupling and ensemble effects
as primary mechanisms responsible for CISS.Comment: 15 pages, 4 figures, plus Supporting Informatio
Enantioselective adsorption on magnetic surfaces
From the beginning of molecular theory, the interplay of chirality and
magnetism has intrigued scientists. There is still the question if
enantiospecific adsorption of chiral molecules occurs on magnetic surfaces.
Enantiomer discrimination was conjectured to arise from chirality-induced spin
separation within the molecules and exchange interaction with the substrate's
magnetization. Here we show that single helical aromatic hydrocarbons undergo
enantioselective adsorption on ferromagnetic cobalt surfaces. Spin and
chirality sensitive scanning tunneling microscopy reveals that molecules of
opposite handedness prefer adsorption onto cobalt islands with opposite
out-of-plane magnetization. As mobility ceases in the final chemisorbed state,
it is concluded that enantioselection must occur in a physisorbed transient
precursor state. State-of-the-art spin-resolved ab initio simulations support
this scenario by refuting enantio-dependent chemisorption energies. These
findings demonstrate that van der Waals interaction should also include
spin-fluctuations which are crucial for molecular magnetochiral processes
ΠΠ»ΠΈΡΠ½ΠΈΠ΅ ΡΠΈΡΠΈΠ½Ρ ΡΠ΅Π·Π° Π½Π° ΠΎΡΠ΅Π²ΡΡ ΠΏΡΠΎΠ΅ΠΊΡΠΈΡ ΡΠΈΠ»Ρ ΡΠ΅Π·Π°Π½ΠΈΡ
Π ΡΡΠ°ΡΡΠ΅ ΠΎΠ±ΠΎΡΠ½ΠΎΠ²ΡΠ²Π°Π΅ΡΡΡ Π²Π»ΠΈΡΠ½ΠΈΠ΅ ΡΠΈΡΠΈΠ½Ρ ΡΠ΅Π·Π° Π½Π° ΠΏΡΠΎΠ΅ΠΊΡΠΈΡ ΡΠΎΡΡΠ°Π²Π»ΡΡΡΠ΅ΠΉ ΡΠΈΠ»Ρ ΡΠ΅Π·Π°Π½ΠΈΡ Π½Π° ΠΎΡΡ Π²ΡΠ°ΡΠ΅Π½ΠΈΡ Π³Π΅ΠΎΡ
ΠΎΠ΄Π°. Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½Π° Π°ΠΊΡΡΠ°Π»ΡΠ½ΠΎΡΡΡ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ. ΠΠ»Ρ ΠΏΠΎΡΡΠ°Π½ΠΎΠ²ΠΊΠΈ ΡΠ΅Π»ΠΈ ΠΈ Π·Π°Π΄Π°Ρ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½Π° ΠΏΡΠΎΠ΅ΠΊΡΠΈΡ ΡΠΎΡΡΠ°Π²Π»ΡΡΡΠ΅ΠΉ ΡΠΈΠ»Ρ ΡΠ΅Π·Π°Π½ΠΈΡ Π½Π° ΠΎΡΡ Π²ΡΠ°ΡΠ΅Π½ΠΈΡ Π³Π΅ΠΎΡ
ΠΎΠ΄Π°. ΠΠ° ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΈΠΈ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½Π½ΠΎΠ³ΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΏΠΎΡΡΡΠΎΠ΅Π½Π° Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΡ ΠΎΡΠ΅Π²ΠΎΠΉ ΠΏΡΠΎΠ΅ΠΊΡΠΈΠΈ ΡΠΈΠ»Ρ ΡΠ΅Π·Π°Π½ΠΈΡ Π½ΠΎΠΆΠ΅Π²ΠΎΠ³ΠΎ ΠΈΡΠΏΠΎΠ»Π½ΠΈΡΠ΅Π»ΡΠ½ΠΎΠ³ΠΎ ΠΎΡΠ³Π°Π½Π° Π³Π΅ΠΎΡ
ΠΎΠ΄Π° (Π 0.Π‘Π) ΠΎΡ ΡΠ°ΡΡΡΠΎΡΠ½ΠΈΡ Ρ
Π½Π° ΠΊΠΎΡΠΎΡΠΎΠ΅ ΠΎΡΠ΄Π°Π»Π΅Π½Π° ΡΠΎΡΠΊΠ° ΠΎΡ ΠΎΡΠΈ Π²ΡΠ°ΡΠ΅Π½ΠΈΡ
Beam Spot Position Measurement at the LEP Collider
A precise knowledge of the beam spot position is required for many physics topics at LEP2. The movement of the beam spot is studied at LEP1 using beam orbit monitors close to the interaction points and compared with measurements from tracks produced in e+e- collisions. The beam orbit monitors are found to follow the beam spot position well, particularly when corrected for movements of nearby quadrupole magnets. Data from the LEP high energy run of November 1995 are also analysed, and projections made for the prospects at LEP2
- β¦