Do wavelets really detect non-Gaussianity in the 4-year COBE data?

We investigate the detection of non-Gaussianity in the 4-year COBE data reported by Pando, Valls-Gabaud & Fang (1998), using a technique based on the discrete wavelet transform. Their analysis was performed on the two DMR faces centred on the North and South Galactic poles respectively, using the Daubechies 4 wavelet basis. We show that these results depend critically on the orientation of the data, and so should be treated with caution. For two distinct orientations of the data, we calculate unbiased estimates of the skewness, kurtosis and scale-scale correlation of the corresponding wavelet coefficients in all of the available scale domains of the transform. We obtain several detections of non-Gaussianity in the DMR-DSMB map at greater than the 99 per cent confidence level, but most of these occur on pixel-pixel scales and are therefore not cosmological in origin. Indeed, after removing all multipoles beyond $\ell = 40$ from the COBE maps, only one robust detection remains. Moreover, using Monte-Carlo simulations, we find that the probability of obtaining such a detection by chance is 0.59. We repeat the analysis for the 53+90 GHz coadded COBE map. In this case, after removing $\ell > 40$ multipoles, two non-Gaussian detections at the 99 per cent level remain. Nevertheless, again using Monte-Carlo simulations, we find that the probability of obtaining two such detections by chance is 0.28. Thus, we conclude the wavelet technique does {\em not} yield strong evidence for non-Gaussianity of cosmological origin in the 4-year COBE data.Comment: 7 pages, 5 figures. Revised version including discussion of orientation sensitivity of the wavelet decomposition. MNRAS submitte

Analytical approach to the transition to thermal hopping in the thin- and thick-wall approximations

The nature of the transition from the quantum tunneling regime at low temperatures to the thermal hopping regime at high temperatures is investigated analytically in scalar field theory. An analytical bounce solution is presented, which reproduces the action in the thin-wall as well as thick-wall limits. The transition is first order for the case of a thin wall while for the thick wall case it is second order.Comment: Latex file, 22 pages, 4 Postscript figure

Kinematical Analogy for Marginal Dyon Decay

We describe a kinematical analogy for the marginal decay of 1/4-BPS dyons in 4-dimensional N=4 string compactifications. In this analogy, the electric and magnetic charges play the role of spatial momenta, the BPS mass plays the role of energy, and 1/2-BPS dyons correspond to massless particles. Using SO(12,1) "Lorentz" invariance and standard kinematical formulae in particle physics, we provide simple derivations of the curves of marginal stability. We also show how these curves map into the momentum ellipsoid, and propose some applications of this analogy.Comment: 10 pages, minor revision

Microphysical, microchemical and adhesive properties of lunar material. 3: Gas interaction with lunar material

Knowledge of the reactivity of lunar material surfaces is important for understanding the effects of the lunar or space environment upon this material, particularly its nature, behavior and exposure history in comparison to terrestrial materials. Adsorptive properties are one of the important techniques for such studies. Gas adsorption measurements were made on an Apollo 12 ultrahigh vacuum-stored sample and Apollo 14 and 15 N2-stored samples. Surface area measurements were made on the latter two. Adsorbate gases used were N2, A, O2 and H2O. Krypton was used for the surface area determinations. Runs were made at room and liquid nitrogen temperature in volumetric and gravimetric systems. It was found that the adsorptive/desorptive behavior was in general significantly different from that of terrestrial materials of similar type and form. Specifically (1) the UHV-stored sample exhibited very high initial adsorption indicative of high surface reactivity, and (2) the N2-stored samples at room and liquid nitrogen temperatures showed that more gas was desorbed than introduced during adsorption, indicative of gas release from the samples. The high reactivity is a scribed cosmic ray track and solar wind damage

Emergence of a non-scaling degree distribution in bipartite networks: a numerical and analytical study

We study the growth of bipartite networks in which the number of nodes in one of the partitions is kept fixed while the other partition is allowed to grow. We study random and preferential attachment as well as combination of both. We derive the exact analytical expression for the degree-distribution of all these different types of attachments while assuming that edges are incorporated sequentially, i.e., a single edge is added to the growing network in a time step. We also provide an approximate expression for the case when more than one edge are added in a time step. We show that depending on the relative weight between random and preferential attachment, the degree-distribution of this type of network falls into one of four possible regimes which range from a binomial distribution for pure random attachment to an u-shaped distribution for dominant preferential attachment

Technology transfer in a horizontally differentiated product-market

This paper considers technology transfer in a Cournot-duopoly market where the firms produce horizontally differentiated products. It turns out that without the threat of imitation from the licensee, the licenser always transfers its best technology. However, the patent licensing contract consists of up-front fixed fee and per unit output royalty for products of neither close substitutes nor isolated. In case the goods are close substitutes then only per unit output royalty is the optimal solution. However, whether the incentive for imitation increases with product differentiation is ambiguous. Hence, with the presence of credible imitation threat, the relation between the likelihood of best technology transfer and product differentiation is not clear always