Null point distribution in global coronal potential field extrapolations

SJE would like to thank the Isle of Man Government for support during her PhD and also for the financial support of the STFC.Magnetic null points are points in space where the magnetic field is zero. Thus, they can be important sites for magnetic reconnection by virtue of the fact that they are weak points in the magnetic field and also because they are associated with topological structures, such as separators, which lie on the boundary between four topologically distinct flux domains and therefore are also locations where reconnection occurs. The number and distribution of nulls in a magnetic field acts as a measure of the complexity of the field. In this article, the numbers and distributions of null points in global potential field extrapolations from high-resolution synoptic magnetograms are examined. Extrapolations from magnetograms obtained with the Michelson Doppler Imager (MDI) are studied in depth and compared with those from high-resolution SOlar Long-time Investigations of the Sun (SOLIS) and Heliospheric Magnetic Imager (HMI). The fall-off in the density of null points with height is found to follow a power law with a slope that differs depending on whether the data are from solar maximum or solar minimum. The distribution of null points with latitude also varies with the cycle as null points form predominantly over quiet-Sun regions and avoid active-region fields. The exception to this rule are the null points that form high in the solar atmosphere, and these null points tend to form over large areas of strong flux in active regions. From case studies of data acquired with the MDI, SOLIS, and HMI, it is found that the distribution of null points is very similar between data sets, except, of course, that there are far fewer nulls observed in the SOLIS data than in the cases from MDI and HMI due to its lower resolution.PostprintPeer reviewe

Influence of previous crops and nematicide treatments on root lesion nematode populations and crop yields

Nous avons étudié au champ l'influence du précédent cultural, de la séquence culturelle et de traitements à l'aldicarbe sur les populations de nematodes des nodosités et sur les rendements de diverses cultures à l'île-du Prince-Édouard. La culture précédente a eu le plus grand impact sur le nombre de nematodes. Les séquences des cultures ont parfois eu une influence sur les populations de nematodes des nodosités (principalement Pratylenchus penetrans) et sur les rendements. Dans les champs commerciaux d'orge (Hordeum vulgare), les nematodes des nodosités étaient plus nombreux lorsque l'orge suivait une culture combinée de trèfle rouge (Trifolium pratense) et de fléole (Phleum pratense) et les nematodes du rabougrissement (Tylenchorynchus spp., principalement T. dubiuset Merlinius spp.) étaient plus nombreux quand l'orge était semée pendant deux années consécutives. La masse de la matière sèche combinée du feuillage et du grain était plus importante lorsque l'orge était semée auprès des pommes de terre (Solanum tuberosum) et cette masse était plus faible avec deux cultures successives d’orge ou avec un mélange de trèfle rouge et de fléole. En conditions expérimentales au champ, les populations de nématodes des nodosités étaient plus élevées dans les racines d’orge lorsque celle-ci était cultivée après des pommes de terre et les rendements en grain étaient plus faibles lorsque l’orge était cultivée pendant deux années consécutives. Les changements dans les populations de nématodes chez la pomme de terre n’étaient pas associés aux séquences débutant avec le blé (Triticum aestivum) ou l’orge que dans les séquences débutant avec les pommes de terre ou le soya (Glycine max). L’aldicarbe a réduit le nombre de nématodes des nodosités en plus d’accroître les rendements en pommes de terre et en soya.A field study assessing the influence of the previous crop, the crop sequence, and aldicarb treatments on root lesion nematode populations and crop yields was carried out in Prince-Edward-Island, Canada. The most recent crop had the greatest impact on nematode numbers. The crop sequences had an influence in some cases on root lesion nematode populations (primarily Pratylenchus penetrans) and on crop yields. In commercial barley (Hordeum vulgare) fields, root lesion nematodes in roots were greatest when barley followed a red clover (Trifolium pratense) timothy (Phleum pratense) ley, and stunt nematodes (Tylenchorhynchus spp., primarily T. dubius, and Merlinius spp.) were more common when barley followed barley. The combined dry weight of foliage and grain was larger when barley was planted after potato (Solanumtuberosum) and smaller when barley followed barley or a red clover-timothy mixture. Under experimental field conditions, root lesion nematode populations were largest in barley roots when barley followed potato and grain yields were smallest when barley followed barley. Changes in nematode populations in potato were not associated with crop sequences. Potato tuber yields were higher in the sequences that began with wheat (Triticum aestivum) or barley than in the sequences that began with potato or soybean (Glycine max). Aldicarb reduced the numbers of root lesion nematodes in roots with concomitant yield increases in potato and soybean

Identification of commonly expressed exoproteins and proteolytic cleavage events by proteomic mining of clinically relevant UK isolates of Staphylococcus aureus

The range of exoproteins and core exoproteome of 14 Staphylococcus aureus isolates representing major lineages associated with asymptomatic carriage and clinical disease in the UK was identified by MS proteomics using a combined database incorporating sequences derived from 39 S. aureus genomes. In all, 632 different proteins were identified and, of these, only 52 (8 %) were found in all 14 isolates whereas 144 (23 %) were found in just a single isolate. Comparison of the observed mass of each protein (based on migration by SDS-PAGE) with its predicted mass (based on amino acid sequence) suggested that 95 % of the proteins identified were not subject to any major post-translational modification. Migration of 5 % of the proteins was not as expected: 1 % of the proteins migrated at a mass greater than predicted, while 4 % appeared to have undergone proteolytic cleavage; these included SsaA2, Aur, SspP, Ebh as well as BlaR1, MecR1, FsH, OatA and LtaS. Intriguingly, a truncated SasG was produced by a single CC8 USA300-like strain. The analysis provided evidence of the marked heterogeneity in protein expression by S. aureus in broth, while yielding a core but narrow common exoproteome

Event by Event Analysis and Entropy of Multiparticle Systems

The coincidence method of measuring the entropy of a system, proposed some time ago by Ma, is generalized to include systems out of equilibrium. It is suggested that the method can be adapted to analyze multiparticle states produced in high-energy collisions.Comment: 13 pages, 2 figure

Excited Baryons in Lattice QCD

We present first results for the masses of positive and negative parity excited baryons calculated in lattice QCD using an O(a^2)-improved gluon action and a fat-link irrelevant clover (FLIC) fermion action in which only the irrelevant operators are constructed with APE-smeared links. The results are in agreement with earlier calculations of N^* resonances using improved actions and exhibit a clear mass splitting between the nucleon and its chiral partner. An correlation matrix analysis reveals two low-lying J^P=(1/2)^- states with a small mass splitting. The study of different Lambda interpolating fields suggests a similar splitting between the lowest two Lambda1/2^- octet states. However, the empirical mass suppression of the Lambda^*(1405) is not evident in these quenched QCD simulations, suggesting a potentially important role for the meson cloud of the Lambda^*(1405) and/or a need for more exotic interpolating fields.Comment: Correlation matrix analysis performed. Increased to 400 configurations. 22 pages, 13 figures, 15 table

Superconductivity in the two dimensional Hubbard Model.

Quasiparticle bands of the two-dimensional Hubbard model are calculated using the Roth two-pole approximation to the one particle Green's function. Excellent agreement is obtained with recent Monte Carlo calculations, including an anomalous volume of the Fermi surface near half-filling, which can possibly be explained in terms of a breakdown of Fermi liquid theory. The calculated bands are very flat around the (pi,0) points of the Brillouin zone in agreement with photoemission measurements of cuprate superconductors. With doping there is a shift in spectral weight from the upper band to the lower band. The Roth method is extended to deal with superconductivity within a four-pole approximation allowing electron-hole mixing. It is shown that triplet p-wave pairing never occurs. Singlet d_{x^2-y^2}-wave pairing is strongly favoured and optimal doping occurs when the van Hove singularity, corresponding to the flat band part, lies at the Fermi level. Nearest neighbour antiferromagnetic correlations play an important role in flattening the bands near the Fermi level and in favouring superconductivity. However the mechanism for superconductivity is a local one, in contrast to spin fluctuation exchange models. For reasonable values of the hopping parameter the transition temperature T_c is in the range 10-100K. The optimum doping delta_c lies between 0.14 and 0.25, depending on the ratio U/t. The gap equation has a BCS-like form and (2*Delta_{max})/(kT_c) ~ 4.Comment: REVTeX, 35 pages, including 19 PostScript figures numbered 1a to 11. Uses epsf.sty (included). Everything in uuencoded gz-compressed .tar file, (self-unpacking, see header). Submitted to Phys. Rev. B (24-2-95

Spectral Properties of the Overlap Dirac Operator in QCD

We discuss the eigenvalue distribution of the overlap Dirac operator in quenched QCD on lattices of size 8^{4}, 10^{4} and 12^{4} at \beta = 5.85 and \beta = 6. We distinguish the topological sectors and study the distributions of the leading non-zero eigenvalues, which are stereographically mapped onto the imaginary axis. Thus they can be compared to the predictions of random matrix theory applied to the \epsilon-expansion of chiral perturbation theory. We find a satisfactory agreement, if the physical volume exceeds about (1.2 fm)^{4}. For the unfolded level spacing distribution we find an accurate agreement with the random matrix conjecture on all volumes that we considered.Comment: 16 pages, 8 figures, final version published in JHE

Using an Observational Framework to investigate adult language input to young children in a naturalistic environment

The correlation between the communicative intent of parents, in terms of their expectation of a response and the response patterns of young children aged 23—25 months during parent—child interactions, was investigated. An Observational Framework was used to code these parameters in interactions between 36 children and their mothers. The children were assigned by cluster analysis to `advanced', `typical' and `delayed' language groups and their responses were coded with respect to the degree of correctness or appropriateness within the interaction. Differences in both the parental response expectations and the children's response patterns across the three clusters are discussed

DN interaction from meson exchange

A model of the DN interaction is presented which is developed in close analogy to the meson-exchange KbarN potential of the Juelich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (rho, omega) exchange and higher-order box diagrams involving D*N, D\Delta, and D*\Delta intermediate states. The coupling of DN to the pi-Lambda_c and pi-Sigma_c channels is taken into account. The interaction model generates the Lambda_c(2595) resonance dynamically as a DN quasi-bound state. Results for DN total and differential cross sections are presented and compared with predictions of an interaction model that is based on the leading-order Weinberg-Tomozawa term. Some features of the Lambda_c(2595) resonance are discussed and the role of the near-by pi-Sigma_c threshold is emphasized. Selected predictions of the orginal KbarN model are reported too. Specifically, it is pointed out that the model generates two poles in the partial wave corresponding to the Lambda(1405) resonance.Comment: 14 pages, 8 figure

Anthropogenic Space Weather

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure