Cloud-to-ground lightning polarity and environmental conditions over the central United States

2007 Summer.Includes bibliographical references (pages 101-109).Related to Atmospheric science papers (Bluebooks).The majority of cloud-to-ground (CG) lightning across the United States lowers negative charge to the ground. However, recent studies have documented storms that produce an abundance of positive CG lightning. These positive storms have been shown to occur in different mesoscale regions on the same days, and in different thermodynamic environments. This study uses radar data, and CG lightning data, to identify positive and negative storms that occurred in the region between the Rocky Mountains and the Mississippi River. The thermodynamic conditions in the environment of these storms are derived from the Rapid Update Cycle model analysis, where the point nearest to the storm, in the direction of storm motion was used. Considerable scatter was present in the final results that limited the extent of the trends seen. Out of all the variables used, cloud base height, dew point, 850-500 mb lapse rate, and warm cloud depth showed the most difference between the positive and negative storms. Positive storms tended to occur with lower cloud base heights, higher dew points, smaller 850-500 mb lapse rates, and lower warm cloud depths. Little trend was seen for CAPE, CIN, freezing level, lifted index, mean relative humidity, mid-level relative humidity, precipitable water 0-3 km wind shear, 0-6 km wind shear, storm relative helicity, and Se. The strength of the differences seen between the positive and negative storms varies with the choice of percent positive used. Differences between the positive and negative storms tended to decrease when 10% was chosen (as compared to 30%), but they increased when 50% was chosen.Supported by the National Science Foundation - ATM-0309303

Towards a direct transition energy measurement of the lowest nuclear excitation in 229Th

The isomeric first excited state of the isotope 229Th exhibits the lowest nuclear excitation energy in the whole landscape of known atomic nuclei. For a long time this energy was reported in the literature as 3.5(5) eV, however, a new experiment corrected this energy to 7.6(5) eV, corresponding to a UV transition wavelength of 163(11) nm. The expected isomeric lifetime is $\tau=$ 3-5 hours, leading to an extremely sharp relative linewidth of Delta E/E ~ 10^-20, 5-6 orders of magnitude smaller than typical atomic relative linewidths. For an adequately chosen electronic state the frequency of the nuclear ground-state transition will be independent from influences of external fields in the framework of the linear Zeeman and quadratic Stark effect, rendering 229mTh a candidate for a reference of an optical clock with very high accuracy. Moreover, in the literature speculations about a potentially enhanced sensitivity of the ground-state transition of $^{229m}$Th for eventual time-dependent variations of fundamental constants (e.g. fine structure constant alpha) can be found. We report on our experimental activities that aim at a direct identification of the UV fluorescence of the ground-state transition energy of 229mTh. A further goal is to improve the accuracy of the ground-state transition energy as a prerequisite for a laser-based optical control of this nuclear excited state, allowing to build a bridge between atomic and nuclear physics and open new perspectives for metrological as well as fundamental studies

BlogForever D3.2: Interoperability Prospects

This report evaluates the interoperability prospects of the BlogForever platform. Therefore, existing interoperability models are reviewed, a Delphi study to identify crucial aspects for the interoperability of web archives and digital libraries is conducted, technical interoperability standards and protocols are reviewed regarding their relevance for BlogForever, a simple approach to consider interoperability in specific usage scenarios is proposed, and a tangible approach to develop a succession plan that would allow a reliable transfer of content from the current digital archive to other digital repositories is presented

Dynamics of single polymers under extreme confinement

We study the dynamics of a single chain polymer confined to a two dimensional cell. We introduce a kinetically constrained lattice gas model that preserves the connectivity of the chain, and we use this kinetically constrained model to study the dynamics of the polymer at varying densities through Monte Carlo simulations. Even at densities close to the fully-packed configuration, we find that the monomers comprising the chain manage to diffuse around the box with a root mean square displacement of the order of the box dimensions over time scales for which the overall geometry of the polymer is, nevertheless, largely preserved. To capture this shape persistence, we define the local tangent field and study the two-time tangent-tangent correlation function, which exhibits a glass-like behavior. In both closed and open chains, we observe reptational motion and reshaping through local fingering events which entail global monomer displacement.Comment: 22 pages, 18 figures, slightly extended version to appear in JSTA

Mixtures of tails in clustered automobile collision claims

Knowledge of the tail shape of claim distributions provides important actuarial information. This paper discusses how two techniques commonly used in assessing the most appropriate underlying distribution can be usefully combined. The maximum likelihood approach is theoretically appealing since it is preferable to many other estimators in the sense of best asymptotic normality. Likelihood based tests are, however, not always capable to discriminate among non-nested classes of distributions. Extremal value theory offers an attractive tool to overcome this problem. It shows that a much larger set of distributions is nested in their tails by the so-called tail parameter. This paper shows that both estimation strategies can be usefully combined when the data generating process is characterized by strong clustering in time and size. We find that the extreme value theory is a useful starting point in detecting the appropriate distribution class. Once that has been achieved, the likelihood-based EM-algorithm is proposed to capture the clustering phenomena. Clustering is particularly pervasive in actuarial data. An empirical application to a four-year data set of Dutch automobile collision claims is therefore used to illustrate the approach

Sovereign bond market reactions to fiscal rules and no-bailout clauses: the Swiss experience

We investigate the political determinants of risk premiums which sub-national governments in Switzerland have to pay for their sovereign bond emissions. For this purpose we analyse financial market data from 288 tradable cantonal bonds in the period from 1981 to 2007. Our main focus is on two different institutional factors. First, many of the Swiss cantons have adopted strong fiscal rules. We find evidence that both the presence and the strength of these fiscal rules contribute significantly to lower cantonal bond spreads. Second, we study the impact of a credible no-bailout regime on the risk premia of potential guarantors. We make use of the Leukerbad court decision in July 2003 which relieved the cantons from backing municipalities in financial distress, thus leading to a fully credible no-bailout regime. Our results show that this break lead to a reduction of cantonal risk premia by about 25 basis points. Moreover, it cut the link between cantonal risk premia and the financial situation of the municipalities in its canton which existed before. This demonstrates that a not fully credible no-bailout commitment can entail high costs for the potential guarantor

Superconductors with Topological Order

We propose a mechanism of superconductivity in which the order of the ground state does not arise from the usual Landau mechanism of spontaneous symmetry breaking but is rather of topological origin. The low-energy effective theory is formulated in terms of emerging gauge fields rather than a local order parameter and the ground state is degenerate on topologically non-trivial manifolds. The simplest example of this mechanism of superconductivty is concretely realized as global superconductivty in Josephson junction arrays.Comment: 4 pages, no figure

Deterministic delivery of remote entanglement on a quantum network

Large-scale quantum networks promise to enable secure communication, distributed quantum computing, enhanced sensing and fundamental tests of quantum mechanics through the distribution of entanglement across nodes. Moving beyond current two-node networks requires the rate of entanglement generation between nodes to exceed their decoherence rates. Beyond this critical threshold, intrinsically probabilistic entangling protocols can be subsumed into a powerful building block that deterministically provides remote entangled links at pre-specified times. Here we surpass this threshold using diamond spin qubit nodes separated by 2 metres. We realise a fully heralded single-photon entanglement protocol that achieves entangling rates up to 39 Hz, three orders of magnitude higher than previously demonstrated two-photon protocols on this platform. At the same time, we suppress the decoherence rate of remote entangled states to 5 Hz by dynamical decoupling. By combining these results with efficient charge-state control and mitigation of spectral diffusion, we are able to deterministically deliver a fresh remote state with average entanglement fidelity exceeding 0.5 at every clock cycle of $\sim$100 ms without any pre- or post-selection. These results demonstrate a key building block for extended quantum networks and open the door to entanglement distribution across multiple remote nodes.Comment: v2 - updated to include relevant citatio

String Fields and the Standard Model

The Cremmer-Scherk mechanism is generalised in a non-Abelian context. In the presence of the Higgs scalars of the standard model it is argued that fields arising from the low energy effective string action may contribute to the mass generation of the observed vector bosons that mediate the electroweak interactions and that future analyses of experimental data should consider the possibility of string induced radiative corrections to the Weinberg angle coming from physics beyond the standard model.Comment: 4 pages, LATEX, no figure