Searches for solar-influenced radioactive decay anomalies using Spacecraft RTGs

Experiments showing a seasonal variation of the nuclear decay rates of a number of different nuclei, and decay anomalies apparently related to solar flares and solar rotation, have suggested that the Sun may somehow be influencing nuclear decay processes. Recently, Cooper searched for such an effect in $^{238}$Pu nuclei contained in the radioisotope thermoelectric generators (RTGs) on board the Cassini spacecraft. In this paper we modify and extend Cooper's analysis to obtain constraints on anomalous decays of $^{238}$Pu over a wider range of models, but these limits cannot be applied to other nuclei if the anomaly is composition-dependent. We also show that it may require very high sensitivity for terrestrial experiments to discriminate among some models if such a decay anomaly exists, motivating the consideration of future spacecraft experiments which would require less precision.Comment: 8 pages, 4 figures (to appear in Astroparticle Physics

Study of the dependence of 198Au half-life on source geometry

We report the results of an experiment to determine whether the half-life of \Au{198} depends on the shape of the source. This study was motivated by recent suggestions that nuclear decay rates may be affected by solar activity, perhaps arising from solar neutrinos. If this were the case then the $\beta$-decay rates, or half-lives, of a thin foil sample and a spherical sample of gold of the same mass and activity could be different. We find for \Au{198}, $(T_{1/2})_{\rm foil}/(T_{1/2})_{\rm sphere} = 0.999 \pm 0.002$, where $T_{1/2}$ is the mean half-life. The maximum neutrino flux at the sample in our experiments was several times greater than the flux of solar neutrinos at the surface of the Earth. We show that this increase in flux leads to a significant improvement in the limits that can be inferred on a possible solar contribution to nuclear decays.Comment: 5 pages, 1 figur

Casimir Effect on the Worldline

We develop a method to compute the Casimir effect for arbitrary geometries. The method is based on the string-inspired worldline approach to quantum field theory and its numerical realization with Monte-Carlo techniques. Concentrating on Casimir forces between rigid bodies induced by a fluctuating scalar field, we test our method with the parallel-plate configuration. For the experimentally relevant sphere-plate configuration, we study curvature effects quantitatively and perform a comparison with the ``proximity force approximation'', which is the standard approximation technique. Sizable curvature effects are found for a distance-to-curvature-radius ratio of a/R >~ 0.02. Our method is embedded in renormalizable quantum field theory with a controlled treatment of the UV divergencies. As a technical by-product, we develop various efficient algorithms for generating closed-loop ensembles with Gaussian distribution.Comment: 27 pages, 10 figures, Sect. 2.1 more self-contained, improved data for Fig. 6, minor corrections, new Refs, version to be published in JHE

QCD Corrections to t anti-b H^- Associated Production in e^+ e^- Annihilation

We calculate the QCD corrections to the cross section of e^+ e^- -> t anti-b H^- and its charge-conjugate counterpart within the minimal supersymmetric extension of the Standard Model. This process is particularly important if m_t b H^+ and e^+ e^- -> H^+ H^- are not allowed kinematically. Large logarithmic corrections that arise in the on-mass-shell scheme of quark mass renormalization, especially from the t anti-b H^- Yukawa coupling for large values of tan(beta), are resummed by adopting the modified minimal-subtraction scheme, so that the convergence behavior of the perturbative expansion is improved. The inclusion of the QCD corrections leads to a significant reduction of the theoretical uncertainties due to scheme and scale dependences.Comment: 21 pages (Latex), 8 figures (Postscript); detailed discussion of scheme and scale dependences adde

A new mammal from the Turonian–Campanian (Upper Cretaceous) Galula Formation, southwestern Tanzania

We here establish a new mammaliaform genus and species, Galulatherium jenkinsi (Mammalia), from the Upper Cretaceous Galula Formation in the Rukwa Rift Basin of southwestern Tanzania. This represents the first named taxon of a mammaliaform from the entire Late Cretaceous of continental Afro-Arabia, an interval of 34 million years. Preliminary study of the holotypic and only known specimen (a partial dentary) resulted in tentative assignation to the Gondwanatheria, a poorly known, enigmatic clade of Late Cretaceous–Paleogene Gondwanan mammals (Krause et al. 2003). The application of advanced imaging (μCT) and visualization techniques permits a more detailed understanding of key anatomical features of the new taxon. It reveals that the lower dentition consisted of a large, procumbent lower incisor and four cheek teeth, all of which were evergrowing (hypselodont). Importantly, all of the teeth appear devoid of enamel. Comparisons conducted with a range of Mesozoic and selected Cenozoic mammaliaform groups document a number of features (e.g., columnar, enamel-less and evergrowing teeth, with relatively simple occlusal morphology) expressed in Galulatherium that are reminiscent of several distantly related groups, making taxonomic assignment difficult at this time. Herein we retain the provisional referral of Galulatherium (RRBP 02067) to Gondwanatheria; it is most similar to sudamericids such as Lavanify and Bharratherium from the Late Cretaceous of Madagascar and India, respectively, in exhibiting relatively simple, high-crowned, columnar cheek teeth. Other features (e.g., enamel-less dentition) are shared with disparate forms such as the Late Jurassic Fruitafossor and toothed xenarthrans (e.g., sloths), here attributed to convergence. Revised analyses of the depositional context for the holotype place it as having lived sometime between the late Turonian and latest Campanian (roughly 91–72 million years ago). This enhanced geochronological context helps to refine the palaeobiogeographical significance of Galulatherium among Cretaceous mammals in general and those from Gondwanan landmasses specifically

Improved tests of extra-dimensional physics and thermal quantum field theory from new Casimir force measurements

We report new constraints on extra-dimensional models and other physics beyond the Standard Model based on measurements of the Casimir force between two dissimilar metals for separations in the range 0.2--1.2 $\mu$m. The Casimir force between an Au-coated sphere and a Cu-coated plate of a microelectromechanical torsional oscillator was measured statically with an absolute error of 0.3 pN. In addition, the Casimir pressure between two parallel plates was determined dynamically with an absolute error of $\approx 0.6$ mPa. Within the limits of experimental and theoretical errors, the results are in agreement with a theory that takes into account the finite conductivity and roughness of the two metals. The level of agreement between experiment and theory was then used to set limits on the predictions of extra-dimensional physics and thermal quantum field theory. It is shown that two theoretical approaches to the thermal Casimir force which predict effects linear in temperture are ruled out by these experiments. Finally, constraints on Yukawa corrections to Newton's law of gravity are strengthened by more than an order of magnitude in the range 56 nm to 330 nm.Comment: Revtex 4, 35 pages, 14 figures in .gif format, accepted for publication in Phys. Rev.

Geometry and material effects in Casimir physics - Scattering theory

We give a comprehensive presentation of methods for calculating the Casimir force to arbitrary accuracy, for any number of objects, arbitrary shapes, susceptibility functions, and separations. The technique is applicable to objects immersed in media other than vacuum, to nonzero temperatures, and to spatial arrangements in which one object is enclosed in another. Our method combines each object's classical electromagnetic scattering amplitude with universal translation matrices, which convert between the bases used to calculate scattering for each object, but are otherwise independent of the details of the individual objects. This approach, which combines methods of statistical physics and scattering theory, is well suited to analyze many diverse phenomena. We illustrate its power and versatility by a number of examples, which show how the interplay of geometry and material properties helps to understand and control Casimir forces. We also examine whether electrodynamic Casimir forces can lead to stable levitation. Neglecting permeabilities, we prove that any equilibrium position of objects subject to such forces is unstable if the permittivities of all objects are higher or lower than that of the enveloping medium; the former being the generic case for ordinary materials in vacuum.Comment: 44 pages, 11 figures, to appear in upcoming Lecture Notes in Physics volume in Casimir physic

Cichlid biogeography: comment and review

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72313/1/j.1467-2979.2004.00148.x.pd

Early above- and below-ground responses of subboreal conifer seedlings to various levels of deciduous canopy removal

We examined the growth of understory conifers, following partial or complete deciduous canopy removal, in a field study established in two regions in Canada. In central British Columbia, we studied the responses of three species (Pseudotsuga menziesii var. glauca (Beissn.) Franco, Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm., and Abies lasiocarpa (Hook.) Nutt.), and in northwestern Quebec, we studied one species (Abies balsamea (L.) Mill.). Stem and root diameter and height growth were measured 5 years before and 3 years after harvesting. Both root and stem diameter growth increased sharply following release but seedlings showed greater root growth, suggesting that in the short term, improvement in soil resource capture and transport, and presumably stability, may be more important than an increase in stem diameter and height growth. Response was strongly size dependent, which appears to reflect greater demand for soil resources as well as higher light levels and greater tree vigour before release for taller individuals. Growth ratios could not explain the faster response generally attributed to true fir species or the unusual swift response of spruces. Good prerelease vigour of spruces, presumably favoured by deciduous canopies, could explain their rapid response to release

ARGONAUT II study of the in vitro activity of plazomicin against carbapenemase-producing klebsiella pneumoniae

Plazomicin was tested against 697 recently acquired carbapenemresistant Klebsiella pneumoniae isolates from the Great Lakes region of the United States. Plazomicin MIC50 and MIC90 values were 0.25 and 1 mg/liter, respectively; 680 isolates (97.6%) were susceptible (MICs of ≤2 mg/liter), 9 (1.3%) intermediate (MICs of 4 mg/liter), and 8 (1.1%) resistant (MICs of>32 mg/liter). Resistance was associated with rmtF-, rmtB-, or armA-encoded 16S rRNA methyltransferases in all except 1 isolate