Atomic Radiative Transitions in Thermo Field Dynamics

In this work we rederive the Lamb-Retherford energy shift for an atomic electron in the presence of a thermal radiation. Using the Dalibard, Dupont-Roc and Cohen-Tannoudji (DDC) formalism, where physical observables are expressed as convolutions of suitable statistical functions, we construct the electromagnetic field propagator of Thermo Field Dynamics in the Coulomb gauge in order to investigate finite temperature effects on the atomic energy levels. In the same context, we also analyze the problem of the ground state stability.Comment: LaTex file, 13 pages, no figures, includes PACS numbers and minor changes in the text where a new section has been adde

A model for the Yield curve

The starting point is an interrogation about the non-broken character of the term structure of interest rates. Some arguments for that smooth character are presented here, all of which are based upon the assumption that market participants - arbitrageurs and speculators - always try to explore any misalignments discovered in the interest market. This led to the basic concept behind the model that the current short-term rate determines most of the value of the rate level for the subsequent period. A linear model describing that simple relationship is assumed and that constitutes the building block from where one can develop the mathematical equations necessary to work with different sets of market data. A number of different yield curves were modelled by adjustment to real market data using this basic model, all of them showing a very high quality of the fits when measured by the non-linear ratio R2. Nevertheless this fact still needs to be confirmed as the examples were drawn from non-independent markets and from a very short time window. The model can be improved by simple addition of a liquidity premium depend only upon the maturity of the rates. However, that improvement sophisticates tremendously the mathematical tractability of any real situation without any assurance that this added cost compensates for the increased quality of the fit. The model is designed around only 3 parameters that can all be interpreted in economic terms. Two of them, in particular, bring a significant improvement over the traditional views frequently extracted from the shape of the yield curve. Provided future tests confirm the high quality of the basic and the improved (with a liquidity premium) models, both are supportive of the expectation hypothesis (EH) and the liquidity premium hypothesis (LPH).

Mass, angular-momentum, and charge inequalities for axisymmetric initial data

We present the key elements of the proof of an upper bound for angular-momentum and charge in terms of the mass for electro-vacuum asymptotically flat axisymmetric initial data sets with simply connected orbit space

Experimental and numerical analysis of the cyclic behaviour of RC beam-column connections with plain reinforcing bars

The information available in the literature about the cyclic behaviour of reinforced concrete elements with plain reinforcing bars is scarce. As a consequence, the influence of bar slippage in elements with plain bars is not yet comprehensively understood. In this paper are presented and discussed the main results of the cyclic tests carried out on five full-scale reinforced concrete beam-column joints with plain bars and without specific detailing for seismic demands. An additional joint specimen with deformed bars was also tested for comparison. Furthermore, numerical models were built to simulate the response of two of the specimens. Particular attention was given to the influence of bar slippage. The results of the conducted analyses underline the importance of accounting for bond-slip in the numerical modelling of elements with plain bars and also highlight the need for specific models to simulate the effects of this mechanism in the presence of plain bars