The health status of Irish honeybee colonies in 2006

peer-reviewedThis study assessed the health status of Irish honeybee colonies and provides a snapshot of the incidence of a number of important colony parasites/pathogens including: the mite Varroa destructor; three associated viruses (deformed wing virus (DWV), acute bee paralysis virus (ABPV) and Kashmir virus (KBV)); the tracheal mite Acarapis woodi; the microsporidian Nosema spp., and the insect Braula coeca. During June/July 2006, 135 samples of adult bees were collected from productive colonies throughout Ireland and standard techniques were used to determine the presence and absence of the parasites and pathogens. Varroa destructor was positively identified in 72.6% of the samples and was widely distributed. Although the samples were analysed for three viruses, DWV, ABPV and KBV, only DWV was detected (frequency = 12.5%). Acarapis woodi and Nosema spp. occurred in approximately 11% and 22% of the samples, respectively, while B. coeca, a wingless dipteran that was once common in Irish honeybee colonies, was very rare (3.7%). Samples where all the pathogens/parasites were jointly absent were statistically under-represented in Leinster and DWV was statistically over-represented in Munster. In Ulster, there was over-representation of the categories where all parasites/pathogens were jointly absent and for A. woodi, and underrepresentation of V. destructor.The project was funded by EU FEOGA and the National Apiculture Programme 2007–2010 of the Department of Agriculture, Food and the Marine

Thermally activated escape rates of uniaxial spin systems with transverse field

Classical escape rates of uniaxial spin systems are characterized by a prefactor differing from and much smaller than that of the particle problem, since the maximum of the spin energy is attained everywhere on the line of constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is applied, a saddle point of the energy is formed, and high, moderate, and low damping regimes (similar to those for particles) appear. Here we present the first analytical and numerical study of crossovers between the uniaxial and other regimes for spin systems. It is shown that there is one HD-Uniaxial crossover, whereas at low damping the uniaxial and LD regimes are separated by two crossovers.Comment: 4 PR pages, 3 figures, final published versio

Field dependence of the temperature at the peak of the ZFC magnetization

The effect of an applied magnetic field on the temperature at the maximum of the ZFC magnetization, $M_{ZFC}$, is studied using the recently obtained analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for the prefactor of the N\'{e}el relaxation time which allow one to precisely calculate the prefactor in the N\'{e}el-Brown model and thus the blocking temperature as a function of the coefficients of the Taylor series expansion of the magnetocrystalline anisotropy. The present calculations indicate that even a precise determination of the prefactor in the N\'{e}el-Brown theory, which always predicts a monotonic decrease of the relaxation time with increasing field, is insufficient to explain the effect of an applied magnetic field on the temperature at the maximum of the ZFC magnetization. On the other hand, we find that the non linear field-dependence of the magnetization along with the magnetocrystalline anisotropy appears to be of crucial importance to the existence of this maximum.Comment: 14 LaTex209 pages, 6 EPS figures. To appear in J. Phys.: Condensed Matte

The effect of ionization on the populations of excited levels of C IV and C V in tokamak edge plasmas

The main populating and depopulating mechanisms of the excited energy levels of ions in plasmas with densities <1023-1024 m-3 are electron collisional excitation from the ion's ground state and radiative decay, respectively, with the majority of the electron population being in the ground state of the ionization stage. Electron collisional ionization is predominately expected to take place from one ground state to that of the next higher ionization stage. However, the question arises as to whether, in some cases, ionization can also affect the excited level populations. This would apply particularly to those cases involving transient events such as impurity influxes in a laboratory plasma. An analysis of the importance of ionization in populating the excited levels of ions in plasmas typical of those found in the edge of tokamaks is undertaken for the C IV and C V ionization stages. The emphasis is on those energy levels giving rise to transitions of most use for diagnostic purposes. Carbon is chosen since it is an important contaminant of JET plasmas; it was the dominant low Z impurity before the installation of the ITER-like wall and is still present in the plasma after its installation. Direct electron collisional ionization both from and to excited levels is considered. Distorted-wave Flexible Atomic Code calculations are performed to generate the required ionization cross sections, due to a lack of atomic data in the literature.Comment: 29 pages, 5 figures. This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics B. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Monte Carlo simulation with time step quantification in terms of Langevin dynamics

For the description of thermally activated dynamics in systems of classical magnetic moments numerical methods are desirable. We consider a simple model for isolated magnetic particles in a uniform field with an oblique angle to the easy axis of the particles. For this model, a comparison of the Monte Carlo method with Langevin dynamics yields new insight in the interpretation of the Monte Carlo process, leading to the implementation of a new algorithm where the Monte Carlo step is time-quantified. The numeric results for the characteristic time of the magnetisation reversal are in excellent agreement with asymptotic solutions which itself are in agreement with the exact numerical results obtained from the Fokker-Planck equation for the Neel-Brown model.Comment: 5 pages, Revtex, 4 Figures include

Accurate Results from Perturbation Theory for Strongly Frustrated S=1/2S=1/2 Heisenberg Spin Clusters

We investigate the use of perturbation theory in finite sized frustrated spin systems by calculating the effect of quantum fluctuations on coherent states derived from the classical ground state. We first calculate the ground and first excited state wavefunctions as a function of applied field for a 12-site system and compare with the results of exact diagonalization. We then apply the technique to a 20-site system with the same three fold site coordination as the 12-site system. Frustration results in asymptotically convergent series for both systems which are summed with Pad\'e approximants. We find that at zero magnetic field the different connectivity of the two systems leads to a triplet first excited state in the 12-site system and a singlet first excited state in the 20-site system, while the ground state is a singlet for both. We also show how the analytic structure of the Pad\'e approximants at $|\lambda| \simeq 1$ evolves in the complex $\lambda$ plane at the values of the applied field where the ground state switches between spin sectors and how this is connected with the non-trivial dependence of the $$ number on the strength of quantum fluctuations. We discuss the origin of this difference in the energy spectra and in the analytic structures. We also characterize the ground and first excited states according to the values of the various spin correlation functions.Comment: Final version, accepted for publication in Physical review

Exploring the dimming event of RW Aur A through multi-epoch VLT/X-Shooter spectroscopy

RW Aur A is a CTTS that has suddenly undergone three major dimming events since 2010. We aim to understand the dimming properties, examine accretion variability, and derive the physical properties of the inner disc traced by the CO ro-vibrational emission at NIR wavelengths (2.3 mic). We compared two epochs of X-Shooter observations, during and after the dimming. We modelled the rarely detected CO bandhead emission in both epochs to examine whether the inner disc properties had changed. The SED was used to derive the extinction properties of the dimmed spectrum and compare the infrared excess between the two epochs. Lines tracing accretion were used to derive the mass accretion rate in both states. The CO originates from a region with physical properties of T=3000 K, N$_{CO}$=1x10$^{21}$ cm$^{-2}$ and vsini=113 km/s. The extinction properties of the dimming layer were derived with the effective optical depth ranging from teff 2.5-1.5 from the UV to the NIR. The inferred mass accretion rate Macc is $1.5x 10^{-8}$ Msun/yr and $\sim 2x 10^{-8}$ Msun/yr after and during the dimming respectively. By fitting the SED, additional emission is observed in the IR during the dimming event from dust grains with temperatures of 500-700K. The physical conditions traced by the CO are similar for both epochs, indicating that the inner gaseous disc properties do not change during the dimming events. The extinction curve is flatter than that of the ISM, and large grains of a few hundred microns are thus required. When we correct for the observed extinction, Macc is constant in the two epochs, suggesting that the accretion is stable and therefore does not cause the dimming. The additional hot emission in the NIR is located at about 0.5 au from the star. The dimming events could be due to a dust-laden wind, a severe puffing-up of the inner rim, or a perturbation caused by the recent star-disc encounter.Comment: Accepted by Astronomy & Astrophysic

Body-size and aerial basking dynamics of the Spiny Softshell (Apalone spinifera) in a human-modified landscape in Tennessee, USA

Spiny Softshells (Apalone spinifera) are found in aquatic environments throughout much of the central-eastern USA. Although this species is widespread throughout much of Tennessee, little is known about Spiny Softshells in the state’s northeastern counties. Further, little work has investigated the role of Spiny Softshell body size on resource use, and the morphometrics of the species in a human-modified ecosystem. Here we present results of a four-month capture and basking observation study conducted in 2004. We investigated whether larger body size was positively associated with presence at limited aerial basking resources that are potentially important for thermoregulation. We found that hoop trap captures positioned next to basking sites, a proxy for aerial basking resource use, were not associated with sex or body size measurements. Opportunistic basking observations revealed most individuals basked in the afternoon. Our study, while short in duration and of low sample size, builds understanding on the body size and intraspecific effects of resource use by Spiny Softshells in a human-modified ecosystem

Development and Application of Strategies to Generate Bacteriophage Resistant Strains for Use in Milk Fermentation Processes

End of Project ReportThe objectives of this project were firstly, the identification of natural phage resistance systems for exploitation, secondly, the development of methodologies to utilise these systems to improve the bacteriophage resistance of starter strains for use in milk fermentation processes, and thirdly, the actual application of these methodologies to improving starter strains. The main conclusions were as follows: Three new natural plasmid (DNA)-associated bacteriophage resistance systems were identified at Moorepark. The detailed genetic makeup of the phage resistance plasmid (pMRC01) was elucidated. Bacteriophages currently evolving in the industrial cheese-making environment were monitored to facilitate the judicious choice of phage resistance systems for use in commercial starter cultures which can more effectively target the documented problematic phage types. Two highly virulent phages targeting important cheese starters were identified in the industrial cheese-making environment. A reliable food-grade method to facilitate the transfer of phage resistance systems to cheese-making starter strains was developed. This is based on bacteriocin immunity-linked phage resistance. Phage resistant cheese starter cultures were developed through natural selection and by molecular manipulation using phage resistance plasmids. The phage resistance plasmid pMRC01 was introduced to 31 cheese starter strains.Department of Agriculture, Food and the Marin