Topics in Modern Quantum Optics

This is the written version of lectures presented at "The 17th Symposium on Theoretical Physics - Applied Field Theory", 29 June - 1 July, 1998, the Sangsan Mathematical Science Building, Seoul National University, Seoul, Korea.Comment: 97 pages, 23 figures, 187 references. Misprints corrected, most figures redrawn and references update

Thermally induced photon splitting

We calculate thermal corrections to the non-linear QED effective action for low-energy photon interactions in a background electromagnetic field. The high-temperature expansion shows that at $T \gg m$ the vacuum contribution is exactly cancelled to all orders in the external field except for a non-trivial two-point function contribution. The high-temperature expansion derived reveals a remarkable cancellation of infrared sensitive contributions. As a result photon-splitting in the presence of a magnetic field is suppressed in the presence of an electron-positron QED-plasma at very high temperatures. In a cold and dense plasma a similar suppression takes place. At the same time Compton scattering dominates for weak fields and the suppression is rarely important in physical situations.Comment: 15 pages, 2 ps figures, Late

Atomic beam correlations and the quantum state of the micromaser

Correlation measurements on the states of two-level atoms having passed through a micromaser at different times can be used to infer properties of the quantum state of the radiation field in the cavity. Long(short) correlation length in time is to some extent associated with super(sub)-Poissonian photon statistics. The correlation length is also an indicator of a phase structure much richer than what is revealed by the usual single-time observables, like the atomic inversion or the Mandel quality factor. In realistic experimental situations the correlations may extend over many times the decay time of the cavity. Our assertions are verified by comparing theoretical calculations with a high-precision Monte-Carlo simulation of the micromaser system.Comment: 4 pages, styles: aps, latex, times, epsf, More physical insight added, title and figures changed, more references. The paper can be retrieved as compressed file called elmfors.maser.ps.Z from http://connect.nbi.dk/pub/lautrup/ or via anonymous ftp at ftp://connect.nbi.dk/pub/lautrup

Stress-driven integration strategies and m-AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces

This is the peer reviewed version of the following article: [Aliguer, I., Carol, I., and Sture, S. (2017) Stress-driven integration strategies and m-AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces. Int. J. Numer. Anal. Meth. Geomech., 41: 918–939. doi: 10.1002/nag.2654.], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nag.2654/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The paper proposes a stress-driven integration strategy for Perzyna-type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity-like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m-AGC tangent operator. This operator is combined with the stress-prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra-step iterations (in physical viscoplasticity), or to a variable time-step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero-thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed.Peer ReviewedPostprint (author's final draft

Frost Resistance of Building Materials : Proceedings of the 2nd Nordic Research Seminar in Lund 1996

Frost destruction of porous building materials is a big problem in the Scandinavian countries, and in many other countries inside and outside Europe, such as U.K., Germany, countries in eastem Europe, U.S.A., Canada, etc. Much research has been devoted to solving the frost destruction problem, especially conceming the destruction of concrete, but also conceming the destruction of clay brick, roofing tile, cellular concrete, natural stone, etc. Nordic researchers have made important contributions in the past; names such as Poul Nerenst in Denmark, Sven Gabriel Bergström and Birger Warris in Sweden, and Jukka Vuorinen in Finland can be mentioned. Previously, frost damage was in most cases of type internai damage occurring when the "stone" was frozen in a more than critically saturated condition. During the last decades, surface scaling of concrete is a growing problem in many countries. The reason is an increased use of deicing salts on roads and bridges. Maybe, surface scaling is a rising problem also for other mineral materials, such as natural stone and renderings. In this case, the reason might be that air pollution causes deposition of substances at the stone surface. Eventually, these interact with moisture and frost to cause surface scaling. The mechanisms behind internal frost damage is fairly weIl understood due to work done in the fourties, fifties and sixties, primarily in the U.S.A. by T.C Powers, R.A. Helmuth and others. The mechanisms behind surface salt scaling is however still largely unknown, But as can be seen in these proceedings, much work is now being done in order to clarify the salt scaling mechanism. A very important step has also been the development of salt scaling test methods, that can be used for a rationaI selection of durable concrete. The purpose of this Nordic research seminar was to get a general view of research going on in the Nordic countries on frost destruction. Naturally, most papers deal with concrete, but there are also some papers on other materials. Researchers from Finland, Denmark Norway and Sweden took part in the seminar. This seminar was the second in order. The first took part in 1993 with only a few participants. Hopefully, there will be a third seminar within a few years time summarizing all the frost research which is now going on in the Nordic countries, or that will start in the near future