Debris and micrometeorite impact measurements in the laboratory

A method was developed to simulate space debris in the laboratory. This method, which is an outgrowth of research in inertial confinement fusion (ICF), uses laser ablation to accelerate material. Using this method, single 60 micron aluminum spheres were accelerated to 15 km/sec and larger 500 micron aluminum spheres were accelerated to 2 km/sec. Also, many small (less than 10 micron diameter) irregularly shaped particles were accelerated to speeds of 100 km/sec

The extended, relativistic hyperon star model

In this paper an equation of state of neutron star matter which includes strange baryons in the framework of Zimanyi and Moszkowski (ZM) model has been obtained. We concentrate on the effects of the isospin dependence of the equation of state constructing for the appropriate choices of parameters the hyperons star model. Numerous neutron star models show that the appearance of hyperons is connected with the increasing density in neutron star interiors. Various studies have indicated that the inclusion of delta meson mainly affects the symmetry energy and through this the chemical composition of a neutron star. As the effective nucleon mass contributes to hadron chemical potentials it alters the chemical composition of the star. In the result the obtained model of the star not only excludes large population of hadrons but also does not reduce significantly lepton contents in the star interior.Comment: 22 pages, revtex4, 13 figure

Cholinergic and dopaminergic effects on prediction error and uncertainty responses during sensory associative learning

Navigating the physical world requires learning probabilistic associations between sensory events and their change in time (volatility). Bayesian accounts of this learning process rest on hierarchical prediction errors (PEs) that are weighted by estimates of uncertainty (or its inverse, precision). In a previous fMRI study we found that low-level precision-weighted PEs about visual outcomes (that update beliefs about associations) activated the putative dopaminergic midbrain; by contrast, precision-weighted PEs about cue-outcome associations (that update beliefs about volatility) activated the cholinergic basal forebrain. These findings suggested selective dopaminergic and cholinergic influences on precision-weighted PEs at different hierarchical levels. Here, we tested this hypothesis, repeating our fMRI study under pharmacological manipulations in healthy participants. Specifically, we performed two pharmacological fMRI studies with a between-subject double-blind placebo-controlled design: study 1 used antagonists of dopaminergic (amisulpride) and muscarinic (biperiden) receptors, study 2 used enhancing drugs of dopaminergic (levodopa) and cholinergic (galantamine) modulation. Pooled across all pharmacological conditions of study 1 and study 2, respectively, we found that low-level precision-weighted PEs activated the midbrain and high-level precision-weighted PEs the basal forebrain as in our previous study. However, we found pharmacological effects on brain activity associated with these computational quantities only when splitting the precision-weighted PEs into their PE and precision components: in a brainstem region putatively containing cholinergic (pedunculopontine and laterodorsal tegmental) nuclei, biperiden (compared to placebo) enhanced low-level PE responses and attenuated high-level PE activity, while amisulpride reduced high-level PE responses. Additionally, in the putative dopaminergic midbrain, galantamine compared to placebo enhanced low-level PE responses (in a body-weight dependent manner) and amisulpride enhanced high-level precision activity. Task behaviour was not affected by any of the drugs. These results do not support our hypothesis of a clear-cut dichotomy between different hierarchical inference levels and neurotransmitter systems, but suggest a more complex interaction between these neuromodulatory systems and hierarchical Bayesian quantities. However, our present results may have been affected by confounds inherent to pharmacological fMRI. We discuss these confounds and outline improved experimental tests for the future

Pikamenetelmät kasvin ravinnetilan kuvaajana

Kasvin ravinnetilaa voidaan tarkastella kasvianalyysin avulla. Kokoomanäytteenä kerätty otos pellon kasveista kuvaa kasvien keskimääräistä ravinnepitoisuutta, mutta sen avulla on vaikea tutkia yksittäisiä kasveja. Lisäksi näytteen oton ja tulosten saamisen välillä kuluu useita päiviä. Kasvianalyysin rinnalle on kehitetty erilaisia pikamittareita, joiden avulla kasvien ravinnetilaa voidaan seurata nopeasti ja tulokset ovat luettavissa välittömästi. Menetelmien lisähyötynä on se, että lisänäytteiden ottaminen on edullista, joten voidaan tarkastella jopa yksittäisiä kasveja. Tässä raportissa selvitettiin viiden pikamenetelmän soveltuvuutta kasvin ravinnetilan kuvaamiseen. Menetelmät olivat lehtivihreämittaus (Atleaf+), kasvin sokeripitoisuuden määritys refraktometrillä, kasvisolukkonesteen pH, väärävärivalokuvaus (Publiclab Infragram) ja mangaanimittaus (NN-Easy55). Aineistona käytettiin OSMO hankkeen 24 koelohkoa ja tuloksia verrattiin perinteisen kasvianalyysin tuloksiin. Analysoitavina kasveina oli viljoja, palkokasveja, rapsia, perunaa ja sipulia. Tulosten perusteella pikamenetelmien ja kasvianalyysin tulosten välillä on hajontaa. Lehtivihreätulokset eivät vastanneet kasvin typpipitoisuutta. Kasvisolukon pH vastasi melko hyvin kasvin kationi-anioni erotusta ja typpipitoisuutta, mutta joukosta löytyi myös selvästi poikkeavia kasveja. Kasvuston sokeripitoisuus vastasi typpipitoisuutta, mutta korrelaatio päti vain kasvilajiryhmittäin. Mangaanimittarin ja kasvuston mangaanipitoisuuksien välillä ei ollut selvää yhteyttä, mutta mangaanimittari kuvaa kasvuston kokemaa stressiä mangaaninpuutoksen seurauksena, joten kasvien ja kasvilajikkeiden mangaaninpuutoksen siedossa saattoi olla eroja. Merkittävä ero pikamenetelmien ja kasvianalyysin välillä on niiden otos: pikamenetelmät analysoivat yksittäisiä kasveja, kasvianalyysinäyte kootaan useista kasveista. Tämän johdosta hajonta kasvipopulaation sisällä on odotettavissa olevaa. Pikamenetelmien luotettavuutta voidaan parantaa lisäämällä analysoitavien kasvien määrää, mutta tämä lisää myös analyysin aikamenekkiä. Yhteenvetona pikamenetelmät eivät korvaa, mutta täydentävät kasvianalyysin tuloksia. Niiden tarkempi hyödyntäminen esimerkiksi lannoituksen tarkentamisessa vaatisi kasvilaji ja kasvuastekohtaisia lisäselvityksiä

Kipsi maanparannusaineena : hyödyt ja haitat maan kasvukunnolle

Kipsiä on käytetty lannoitteena ja maanparannusaineena vuosisatojen ajan. Kipsin vaikutus perustuu sen sisältämään kalsiumiin ja rikkiin. Lannoitusvaikutuksen lisäksi kipsiä voidaan käyttää vähentämään maaperän korkeita magnesium- ja alumiinipitoisuuksia ja kehittämään maan rakennetta. Syrjäyttäessään muita kationeja maaperästä kipsi lisää kuitenkin myös kaliumin ja magnesiumin huuhtoutumista, mikä voi pahentaa näiden puutosta. Korkeilla käyttömäärillä kipsi voi häiritä maan biologista toimintaa. Tässä raportissa käydään läpi kipsin tutkimuskirjallisuutta, OSMO koelohkojen tuloksia kipsilisäyksen vaikutuksista maan kasvukuntoon sekä arvioidaan kipsin soveltuvuutta 1068 lohkon viljavuusanalyysiaineiston perusteella. Tulosten perusteella kipsistä ei havaittu haittoja maaperän mikrobiaktiivisuudelle, maan ravinnesuhteille tai kasvien ravinteiden otolle, mikäli sitä käytetään maltillisia määriä savimailla, joissa magnesiumia on runsaasti. Kipsi toimi tulosten perusteella myös rikkilannoitteena ja nosti maaperän rikkitasoja useaksi vuodeksi. Ongelmia saattaa muodostua, jos kipsiä käytetään pelloilla, joissa on valmiiksi magnesiumin tai kaliumin puutetta. Tilakohtaisen tarkastelun perusteella kipsi soveltuu tilasta riippuen 0-50 % lohkoista ja siitä voi olla selvää haittaa 0-73 % lohkoista tilan peltojen tilanteesta riippuen. Kipsin hyötyjen maksimoimiseksi kipsikäsittely kannattaa kohdentaa korkean magnesiumpitoisuuden savipelloille, joissa on puutetta rikistä

The nucleon and mesons effective masses in the Relativistic Mean-Field Theory

Nucleon and meson effective masses in the nonlinear Relativistic Mean - Field Theory (RMF) introducing a nonlinear omega - rho and sigma coupling motivated by the Quark Meson Coupling model (QMC) is explored. It is shown that, in contrast to the usual Walecka model, not only the effective nucleon mass m_{eff,N} but also the effective sigma, rho meson masses (m_{eff, sigma}, m_{eff, rho}) and the effective omega meson mass m_{eff, omega} are nucleon density dependent.Comment: 11 pages, iop latex2e, 7 colour figures, revised version of nucl-th/0011084, accepted to Journal of Physics G: Nuclear and Particle, presented on "Mesons & Light Nuclei '01", Prague, June 200

Quantum jumps induced by the center-of-mass motion of a trapped atom

We theoretically study the occurrence of quantum jumps in the resonance fluorescence of a trapped atom. Here, the atom is laser cooled in a configuration of level such that the occurrence of a quantum jump is associated to a change of the vibrational center-of-mass motion by one phonon. The statistics of the occurrence of the dark fluorescence period is studied as a function of the physical parameters and the corresponding features in the spectrum of resonance fluorescence are identified. We discuss the information which can be extracted on the atomic motion from the observation of a quantum jump in the considered setup

Cooling atomic motion with quantum interference

We theoretically investigate the quantum dynamics of the center of mass of trapped atoms, whose internal degrees of freedom are driven in a $\Lambda$-shaped configuration with the lasers tuned at two-photon resonance. In the Lamb-Dicke regime, when the motional wave packet is well localized over the laser wavelenght, transient coherent population trapping occurs, cancelling transitions at the laser frequency. In this limit the motion can be efficiently cooled to the ground state of the trapping potential. We derive an equation for the center-of-mass motion by adiabatically eliminating the internal degrees of freedom. This treatment provides the theoretical background of the scheme presented in [G. Morigi {\it et al}, Phys. Rev. Lett. {\bf 85}, 4458 (2000)] and implemented in [C.F. Roos {\it et al}, Phys. Rev. Lett. {\bf 85}, 5547 (2000)]. We discuss the physical mechanisms determining the dynamics and identify new parameters regimes, where cooling is efficient. We discuss implementations of the scheme to cases where the trapping potential is not harmonic.Comment: 11 pages, 3 figure

Resonance fluorescence of a trapped three-level atom

We investigate theoretically the spectrum of resonance fluorescence of a harmonically trapped atom, whose internal transitions are $\Lambda$--shaped and driven at two-photon resonance by a pair of lasers, which cool the center--of--mass motion. For this configuration, photons are scattered only due to the mechanical effects of the quantum interaction between light and atom. We study the spectrum of emission in the final stage of laser--cooling, when the atomic center-of-mass dynamics is quantum mechanical and the size of the wave packet is much smaller than the laser wavelength (Lamb--Dicke limit). We use the spectral decomposition of the Liouville operator of the master equation for the atomic density matrix and apply second order perturbation theory. We find that the spectrum of resonance fluorescence is composed by two narrow sidebands -- the Stokes and anti-Stokes components of the scattered light -- while all other signals are in general orders of magnitude smaller. For very low temperatures, however, the Mollow--type inelastic component of the spectrum becomes visible. This exhibits novel features which allow further insight into the quantum dynamics of the system. We provide a physical model that interprets our results and discuss how one can recover temperature and cooling rate of the atom from the spectrum. The behaviour of the considered system is compared with the resonance fluorescence of a trapped atom whose internal transition consists of two-levels.Comment: 11 pages, 4 Figure

Line Graphs of Weighted Networks for Overlapping Communities

In this paper, we develop the idea to partition the edges of a weighted graph in order to uncover overlapping communities of its nodes. Our approach is based on the construction of different types of weighted line graphs, i.e. graphs whose nodes are the links of the original graph, that encapsulate differently the relations between the edges. Weighted line graphs are argued to provide an alternative, valuable representation of the system's topology, and are shown to have important applications in community detection, as the usual node partition of a line graph naturally leads to an edge partition of the original graph. This identification allows us to use traditional partitioning methods in order to address the long-standing problem of the detection of overlapping communities. We apply it to the analysis of different social and geographical networks.Comment: 8 Pages. New title and text revisions to emphasise differences from earlier paper