A facility for investigation of multiple hadrons at cosmic-ray energies

An experimental arrangement for studying multiple hadrons produced in high-energy hadron-nucleus interactions is under construction at the university of Turku. The method of investigation is based on the detection of hadrons arriving simultaneously at sea level over an area of a few square meters. The apparatus consists of a hadron spectrometer with position-sensitive detectors in connection with a small air shower array. The position resolution using streamer tube detectors will be about 10 mm. Energy spectra of hadrons or groups of simultaneous hadrons produced at primary energies below 10 to the 16th power eV can be measured in the energy range 1 to 2000 GeV

Investigation of cosmic rays in very short time scales

A fast databuffer system, where cosmic ray events in the Turku hadron spectrometer, including particle arrival times are recorded with time resolution of 100 ns was constructed. The databuffer can be read continuously by a microprocessor, which preanalyzes the data and transfers it to the main computer. The time span, that can be analyzed in every detail, is a few seconds. The high time resolution enables a study of time correlated groups of high energy particles. In addition the operational characteristics of the spectrometer can be monitored in detail

Spectral analysis of the Forbush decrease of 13 July 1982

The maximum entropy method has been applied in the spectral analysis of high-energy cosmic-ray intensity during the large Forbush event of July 13, 1982. An oscillation with period of about 2 hours and amplitude of 1 to 3% was found to be present during the decrease phase. This oscillation can be related to a similar periodicity in the magnetospheric field. However, the variation was not observed at all neutron monitor stations. In the beginning of the recovery phase, the intensity oscillated with a period of about 10 hours and amplitude of 3%

Observations of cosmic-ray modulations in the fall, 1984

Modulation of cosmic-ray energy spectrum was studied by using the Turku double neutron monitor. The multiplicity region of detected neutrons produced by cosmic ray hadrons in the monitor was divided into seven categories corresponding to mean energies 0.1, 0.3, 1.0, 3.2, 8.6, 21, and 94 GeV of hadrons at sea level. Based on 24-hour frequencies, a statistical analysis showed that modulation of the intensity in all categories occurred during several periods in the fall 1984. The magnitude of the variation was a few per cent

Conductance oscillations in metallic nanocontacts

We examine the conductance properties of a chain of Na atoms between two metallic leads in the limit of low bias. Resonant states corresponding to the conductance channel and the local charge neutrality condition cause conductance oscillations as a function of the number of atoms in the chain. Moreover, the geometrical shape of the contact leads influences the conductivity by giving rise to additional oscillations as a function of the lead opening angle.Peer reviewe

Multigrid method for electronic structure calculations

A general real-space multigrid algorithm for the self-consistent solution of the Kohn-Sham equations appearing in the state-of-the-art electronic-structure calculations is described. The most important part of the method is the multigrid solver for the Schrödinger equation. Our choice is the Rayleigh quotient multigrid method (RQMG), which applies directly to the minimization of the Rayleigh quotient on the finest level. Very coarse correction grids can be used, because there is, in principle, no need to represent the states on the coarse levels. The RQMG method is generalized for the simultaneous solution of all the states of the system using a penalty functional to keep the states orthogonal. The performance of the scheme is demonstrated by applying it in a few molecular and solid-state systems described by nonlocal norm-conserving pseudopotentials.Peer reviewe

Gradient correction for positron states in solids

First-principles calculations of positron-annihilation characteristics in solids are usually based on the local-density approximation (LDA) for positron-electron correlation. The LDA systematically overestimates the annihilation rate. As a remedy we introduce a generalized gradient approximation (GGA). Our results for several metals and semiconductors show that the GGA systematically improves the predictive power of positron lifetime calculations over those based on the LDA. We compare also the resulting positron energy levels in solids with data from slow-positron experiments.Peer reviewe

Imprints of latitude, host taxon, and decay stage on fungus-associated arthropod communities

Interactions among fungi and insects involve hundreds of thousands of species. While insect communities on plants have formed some of the classic model systems in ecology, fungus-based communities and the forces structuring them remain poorly studied by comparison. We characterize the arthropod communities associated with fruiting bodies of eight mycorrhizal basidiomycete fungus species from three different orders along a 1200-km latitudinal gradient in northern Europe. We hypothesized that, matching the pattern seen for most insect taxa on plants, we would observe a general decrease in fungal-associated species with latitude. Against this backdrop, we expected local communities to be structured by host identity and phylogeny, with more closely related fungal species sharing more similar communities of associated organisms. As a more unique dimension added by the ephemeral nature of fungal fruiting bodies, we expected further imprints generated by successional change, with younger fruiting bodies harboring communities different from older ones. Using DNA metabarcoding to identify arthropod communities from fungal fruiting bodies, we found that latitude left a clear imprint on fungus-associated arthropod community composition, with host phylogeny and decay stage of fruiting bodies leaving lesser but still-detectable effects. The main latitudinal imprint was on a high arthropod species turnover, with no detectable pattern in overall species richness. Overall, these findings paint a new picture of the drivers of fungus-associated arthropod communities, suggesting that latitude will not affect how many arthropod species inhabit a fruiting body but, rather, what species will occur in it and at what relative abundances (as measured by sequence read counts). These patterns upset simplistic predictions regarding latitudinal gradients in species richness and in the strength of biotic interactions.Peer reviewe

Calculation of positron states and annihilation in solids: A density-gradient-correction scheme

The generalized gradient correction method for positron-electron correlation effects in solids [B. Barbiellini et al., Phys. Rev. B 51, 7341 (1995)] is applied in several test cases. The positron lifetime, energetics, and momentum distribution of the annihilating electron-positron pairs are considered. The comparison with experiments shows systematic improvement in the predictive power of the theory compared to the local-density approximation results for positron states and annihilation characteristics.Peer reviewe