Fast visual tracking and localization in multi-agent systems

In this paper an implementation of an algorithm for fast visual tracking and localization of mobile agents has been described. Based on an extremely rapid method for visual detection of an object, described localization strategy provides a real time solution suitable for the design of multi-agent control schemes. The agents tracking and localization is carried out through five differently trained cascades of classifiers that process images captured by cameras mounted on agents. In this way, each agent is able to determine relative positions and orientations of all other agents performing tasks in its field of view. The described localization method is suitable for applications involving robot formations. Performance of the proposed method has been demonstrated on a laboratory setup composed of two mobile robot platforms

Diffusive energy transport in the S=1 Haldane chain compound AgVP2S6

We present the results of measurements of the thermal conductivity $\kappa$ of the spin S=1 chain compound AgVP_2S_6 in the temperature range between 2 and 300 K and with the heat flow directed either along or perpendicular to the chain direction. The analysis of the anisotropy of the heat transport allowed for the identification of a small but non-negligible magnon contribution $\kappa_m$ along the chains, superimposed on the dominant phonon contribution $\kappa_ph$. At temperatures above about 100 K the energy diffusion constant D_E(T), calculated from the $\kappa_m(T)$ data, exhibits similar features as the spin diffusion constant D_S(T), previously measured by NMR. In this regime, the behaviour of both transport parameters is consistent with a diffusion process that is caused by interactions inherent to one-dimensional S=1 spin systems.Comment: 6 pages, 4 figure

Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18

The low-temperature elementary spin excitations in the AFM molecular wheel Fe18 were studied experimentally by inelastic neutron scattering and theoretically by modern numerical methods, such as dynamical density matrix renormalization group or quantum Monte Carlo techniques, and analytical spin-wave theory calculations. Fe18 involves eighteen spin-5/2 Fe(III) ions with a Hilbert space dimension of 10^14, constituting a physical system that is situated in a region between microscopic and macroscopic. The combined experimental and theoretical approach allowed us to characterize and discuss the magnetic properties of Fe18 in great detail. It is demonstrated that physical concepts such as the rotational-band or L&E-band concepts developed for smaller rings are still applicable. In particular, the higher-lying low-temperature elementary spin excitations in Fe18 or AFM wheels in general are of discrete antiferromagnetic spin-wave character.Comment: 16 pages, 10 figure

Observation of magnetic fragmentation in spin ice

Fractionalised excitations that emerge from a many body system have revealed rich physics and concepts, from composite fermions in two-dimensional electron systems, revealed through the fractional quantum Hall effect, to spinons in antiferromagnetic chains and, more recently, fractionalisation of Dirac electrons in graphene and magnetic monopoles in spin ice. Even more surprising is the fragmentation of the degrees of freedom themselves, leading to coexisting and a priori independent ground states. This puzzling phenomenon was recently put forward in the context of spin ice, in which the magnetic moment field can fragment, resulting in a dual ground state consisting of a fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic monopole crystal. Here we show, by means of neutron scattering measurements, that such fragmentation occurs in the spin ice candidate Nd$_2$Zr$_2$O$_7$. We observe the spectacular coexistence of an antiferromagnetic order induced by the monopole crystallisation and a fluctuating state with ferromagnetic correlations. Experimentally, this fragmentation manifests itself via the superposition of magnetic Bragg peaks, characteristic of the ordered phase, and a pinch point pattern, characteristic of the Coulomb phase. These results highlight the relevance of the fragmentation concept to describe the physics of systems that are simultaneously ordered and fluctuating.Comment: accepted in Nature Physic

Application of the surface potential data to elucidate interfacial equilibrium at ceria/aqueous electrolyte interface

Interfacial properties of ceria (CeO2) nanoparticles and highly organized ceria crystal planes {111} and {100} in the aqueous electrolyte solution were studied. It was confirmed by high resolution electron spectroscopy that a primary ceria nanoparticle consists mostly of two crystal planes {111} and {100} with different surface sites exposed to the aqueous electrolyte solution. Interfacial properties of ceria nanoparticles are directly related to the reactivity and surface densities of existing surface sites. However, surface characterization (potentiometric titrations and electrophoretic measurements) provides only some kind of average surface properties i.e. average surface charge densities and surface potentials. The point of zero charge (pHpzc) of ceria nanoparticles was measured to be between 6.4 and 8.7, depending on the electrolyte concentration, and the isoelectric point at pHiep = 6.5. With the purpose of understanding ceria nanoparticles surface charging the inner surface potentials of ceria macro crystal planes {111} and {100} were measured for the first time, by means of single crystal electrodes, as a function of pH and ionic strength. The inner surface potential directly affects the state of ionic species bound to a certain surface plane and is thus an essential parameter governing interfacial equilibrium. From the measured Ψ 0(pH) data and applying the Multi Site Complexation Model the thermodynamic equilibrium constants of doubly-coordinated ≡Ce2-OH (at the {100} ceria crystal plane) as well as singly-coordinated ≡Ce1-OH and triply-coordinated ≡Ce3-OH (at the {111} ceria crystal plane) were evaluated. The Ψ 0(pH) function differs for two examined ceria planes, however the inner surface potentials of both planes depend on ionic strength having a broad electroneutrality region between pH = 6 and pH = 9

Kuudesluokkalaisten oppimiskokemuksia ryhmätyöstä Yrityskylä-oppimisympäristössä

Tiivistelmä. Tämä laadullinen tapaustutkimus koskee ryhmätyötaitoja, joita oli mahdollista oppia Yrityskylä-oppimiskokonaisuuden aikana. Tutkimuksen tarkoituksena oli selvittää, miten Yrityskylän oppimateriaaleissa esiintyvä ryhmätyötaitoihin liittyvä sisäisen yrittäjyyden tavoite toteutuu oppimiskokonaisuuden aikana. Tutkimusjoukkona oli 39 Yrityskylä-oppimiskokonaisuuteen osallistuvaa kuudesluokkalaista oppilasta. Tarkastelun kohteena olivat kuudesluokkalaisten käsitykset ryhmätyöstä ja ryhmätyötaidoista. Tutkimusaineisto kerättiin avoimen- ja strukturoidun kyselylomakkeen avulla. Kandidaatin tutkielmassa jaoteltiin Yrityskylän oppimateriaaleissa esiintyviä oppimistavoitteita sisäiseen-, ulkoiseen-, ja omaehtoiseen yrittäjyyteen. Oppimateriaaleista löydettiin yksi sisäisen yrittäjyyden tavoite. Pro gradu -tutkielma rajattiin koskemaan tätä sisäisen yrittäjyyden tavoitetta, joka edelleen rajattiin käsittelemään ryhmätyötä ja ryhmätyötaitoja. Yrittäjyyskasvatus on kasvattamista yrittäjämäiseen asenteeseen ja aktiiviseen kansalaisuuteen. Se on oma aihealueensa myös Perusopetuksen opetussuunnitelman perusteissa Yhteiskuntaopin oppisisällöissä sekä laaja-alaisissa osaamisen tavoitteissa. Yrittäjyyskasvatus korostaa sisäistä yrittäjyyttä, jossa tärkeää on muun muassa luovuuden, oma-aloitteisuuden ja pitkäjänteisyyden vahvistaminen sekä itsensä arvostaminen ja yhteistyön tekeminen. Yrityskylä on Taloudellisen tiedotustoimisto ry:n kehittämä, maailmanlaajuisesti arvostettu suomalainen koulutusinnovaatio, joka on suunnattu kuudesluokkalaisille oppilaille. Yrityskylä on pienoisyhteiskunta, jossa oppilaan vierailevat yhden päivän ajan. Vierailun aikana he toimivat tämän pienoisyhteiskunnan jäseninä harjoitellen yritystoimintaa ja kuluttamista. Yrityskylässä oppilailla on ammatit ja palkallaan he voivat ostaa hyödykkeitä toisista yrityksistä vapaa-ajallaan. Oppimiskokonaisuuteen kuuluu myös oppimateriaalit kymmeneen Yrityskylä-päivää edeltävään oppituntiin, jotka pohjustavat vierailua. Näiden oppituntien aikana oppilaat oppivat erilaisia asioita yhteiskunnasta, liittyen esimerkiksi talouteen, verotukseen, työntekoon ja kaupankäyntiin. Tämän tutkimuksen tulos on, että Yrityskylässä vierailevien oppilaiden käsitykset ryhmätyöstä ja ryhmätyötaidoista eivät merkittävästi muutu oppimiskokonaisuuden aikana. Tämä käy ilmi avoimen kyselylomakkeen vastauksista. Kuitenkin strukturoidun kyselylomakkeen vastakset osoittavat, että oppilaiden oman kokemuksen mukaan ryhmätyötaidot kehittyvät. Avoimen kyselylomakkeen vastauksissa esiintyi toistuvasti samoja termejä ja teemoja, joista selviää, mitä asioita oppilaat pitävät tärkeinä ryhmätyöhön ja ryhmätyötaitoihin liittyen. Toistuvia teemoja olivat auttavaisuus, muiden huomioiminen, kuunteleminen, kaikkien kanssa toimeen tuleminen sekä yhteistyö

Tuning the spin Hamiltonian of NENP by external pressure: a neutron scattering study

We report an inelastic neutron scattering study of antiferromagnetic spin dynamics in the Haldane chain compound Ni(C2H8N2)2NO2ClO4 (NENP) under external hydrostatic pressure P = 2.5 GPa. At ambient pressure, the magnetic excitations in NENP are dominated by a long-lived triplet mode with a gap which is split by orthorhombic crystalline anisotropy into a lower doublet centered at $\Delta_\perp\approx$ 1.2meV and a singlet at $\Delta_\parallel\approx$ 2.5meV. With pressure we observe appreciable shifts in these levels, which move to $\Delta_\perp{(2.5GPa)}\approx$ 1.45 meV and $\Delta_\parallel(2.5GPa)\approx$ 2.2meV. The dispersion of these modes in the crystalline c-direction perpendicular to the chain was measured here for the first time, and can be accounted for by an interchain exchange J'_c approximately 3e-4*J which changes only slightly with pressure. Since the average gap value $\Delta_H\approx$ 1.64 meV remains almost unchanged with P, we conclude that in NENP the application of external pressure does not affect the intrachain coupling J appreciably, but does produce a significant decrease of the single-ion anisotropy constant from D/J = 0.16(2) at ambient pressure to D/J = 0.09(7) at P = 2.5 GPa.Comment: LaTeX file nenp_p.tex, 10 pages, 1 table, 5 figures. Submitted to Phys. Rev.