A Numerical General Circulation Experiment for the Atmosphere of Mars

Numerical model for simulating general circulation of atmosphere of Mar

Inhibition of the dynamical Casimir effect with Robin boundary conditions

We consider a real massless scalar field in 3+1 dimensions satisfying a Robin boundary condition at a nonrelativistic moving mirror. Considering vacuum as the initial field state, we compute explicitly the number of particles created per unit frequency and per unit solid angle, exhibiting in this way the angular dependence of the spectral distribution. The well known cases of Dirichlet and Neumann boundary conditions may be reobtained as particular cases from our results. We show that the particle creation rate can be considerably reduced (with respect to the Dirichlet and Neumann cases) for particular values of the Robin parameter. Our results extend for 3+1 dimensions previous results found in the literature for 1+1 dimensions. Further, we also show that this inhibition of the dynamical Casimir effect occurs for different angles of particle emission.Comment: 18 pages, 3 figure

Hot rolled high Al containing steels as a replacement for the control rolled high strength low alloy (HSLA) steels

The extent to which Al and Nb can be used to improve the properties of hot rolled steels has been investigated with the aim of obtaining mechanical properties similar to those given by the more expensive, control rolled or normalised route, eg. API X52 line pipe. Three steels with 0.02%Al, 0.16%Al and 0.16%Al, 0.018%Nb have been examined and their strength and impact behaviour obtained. The 0.16%Al steel had a similar strength to the 0.02%Al containing steel∼300MPa, but better impact behaviour (30-40°C lower 54J, ITT) with an impact transition temperature (ITT) of −90°C which from previous work will be due to a refinement of the grain boundary carbides. The present work shows that the addition of Nb to this high Al containing steel, although beneficial to strength, giving a lower yield strength (LYS) of 385 MPa, close to that given by some of the control rolled steels gives very poor impact behaviour with a 54J ITT of only −20°C. The improvement of strength is mainly a result of precipitation hardening by NbCN with some benefit from grain refinement while the deterioration of impact behaviour might be due to the presence of lower transformation products or coarser carbides. Further work is required to positively clarify the cause of this deterioration and to explore further options in achieving the aim of obtaining a hot rolled steel with strength in the range 350-400MPa and 54J ITT of −50°C

On thermal nucleation of quark matter in compact stars

The possibility of a hadron-quark phase transition in extreme astrophysical phenomena such as the collapse of a supernova is not discarded by the modern knowledge of the high-energy nuclear and quark-matter equations of state. Both the density and the temperature attainable in such extreme processes are possibly high enough to trigger a chiral phase transition. However, the time scales involved are an important issue. Even if the physical conditions for the phase transition are favorable (for a system in equilibrium), there may not be enough time for the dynamical process of phase conversion to be completed. We analyze the relevant time scales for the phase conversion via thermal nucleation of bubbles of quark matter and compare them to the typical astrophysical time scale, in order to verify the feasibility of the scenario of hadron-quark phase conversion during, for example, the core-collapse of a supernova.Comment: 6 pages, 4 figures, talk given at the International Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200

A local and renormalizable framework for the gauge-invariant operator Amin⁡2A^2_{\min} in Euclidean Yang-Mills theories in linear covariant gauges

We address the issue of the renormalizability of the gauge-invariant non-local dimension-two operator $A^2_{\rm min}$, whose minimization is defined along the gauge orbit. Despite its non-local character, we show that the operator $A^2_{\rm min}$ can be cast in local form through the introduction of an auxiliary Stueckelberg field. The localization procedure gives rise to an unconventional kind of Stueckelberg-type action which turns out to be renormalizable to all orders of perturbation theory. In particular, as a consequence of its gauge invariance, the anomalous dimension of the operator $A^2_{\rm min}$ turns out to be independent from the gauge parameter $\alpha$ entering the gauge-fixing condition, being thus given by the anomalous dimension of the operator $A^2$ in the Landau gauge.Comment: 35 pages; v2: ref. adde