Relaxation rates of the linearized Uehling-Uhlenbeck equation for bosons

We linearize the Uehling-Uhlenbeck equation for bosonic gases close to thermal equilibrium under the assumption of a contact interaction characterized by a scattering length a. We show that the spectrum of relaxation rates is similar to that of a classical hard-sphere gas. However, the relaxation rates show a significant dependence on the fugacity z of the gas, increasing by as much as 60% of their classical value for z approaching 1. The relaxation modes are also significantly altered at higher values of z. The relaxation rates and modes are determined by the eigenvalues and eigenvectors of a Fredholm integral operator of the second kind. We derive an analytical form for the kernel of this operator and present numerical results for the first few eigenvalues and eigenvectors.Robert A. Welch Foundation F-1051Physic

Two-body recombination in a quantum mechanical lattice gas: Entropy generation and probing of short-range magnetic correlations

We study entropy generation in a one-dimensional (1D) model of bosons in an optical lattice experiencing two-particle losses. Such heating is a major impediment to observing exotic low temperature states, and "simulating" condensed matter systems. Developing intuition through numerical simulations, we present a simple empirical model for the entropy produced in this 1D setting. We also explore the time evolution of one and two particle correlation functions, showing that they are robust against two-particle loss. Because of this robustness, induced two-body losses can be used as a probe of short range magnetic correlations.Comment: 6 pages, 3 figures - v4, published versio

"Light from chaos" in two dimensions

We perform a Monte-Carlo study of the lattice two-dimensional gauged XY-model. Our results confirm the strong-coupling expansion arguments that for sufficiently small values of the spin-spin coupling the ``gauge symmetry breaking" terms decouple and the long-distance physics is that of the unbroken pure gauge theory. We find no evidence for the existence, conjectured earlier, of massless states near a critical value of the spin-spin coupling. We comment on recent remarks in the literature on the use of gauged XY-models in proposed constructions of chiral lattice gauge theories.Comment: 6 pages, 7 figure

AdS/CFT and large-N volume independence

We study the Eguchi-Kawai reduction in the strong-coupling domain of gauge theories via the gravity dual of N=4 super-Yang-Mills on R^3xS^1. We show that D-branes geometrize volume independence in the center-symmetric vacuum and give supergravity predictions for the range of validity of reduced large-N models at strong coupling.Comment: 4 pages, 2 figures; references and comments adde

Walter Asmus: Richard Kroner (1884-1974). Ein Philosoph und Pädagoge unter dem Schatten Hitlers. Bern/Frankfurt a.M.: Lang 1990. [Rezension]

Rezension von: Walter Asmus: Richard Kroner (1884-1974). Ein Philosoph und Pädagoge unter dem Schatten Hitlers. Bern/Frankfurt a.M.: Lang 1990. 188 S

H.F. Hauff Pruner Housing & Ergonomics

The technology of electric tree pruners in the current agricultural market has many engineering problems, including; a deficit in power output, excessive overheating, and ergonomics. The 3-man pruner team has coordinated with H.F. Hauff Co. Inc., an agricultural equipment company owned by Neil Hauff, to produce an electric pruner prototype which addresses these problems. The methods used to design the optimal pruner prototype includes traditional engineering stress analysis, force flow analysis, finite element software, and Solidworks modeling software. The construction of the pruner involved manual machining methods and C.N.C. (Computerized Numerical Control) mill technology. During the design process, the team learned advanced analysis practices, the relationships between torque and linear output, work fixture design, product design practices, and found that slight modifications to geometry caused a force amplification effect. With the help of Neil, and his staff, the pruner team gained an appreciation and insight into the professional design process and the relationship between part complexity and fabrication time. The finished prototype was able to meet the initially established design requirements of the pruner. However, the design is still limited with regards power output and operation temperature. The design and analysis performed for this project has made it possible for further optimization of the current prototype and some engineering problems of current electric pruners were addressed and fixed. Weaknesses of the design include a high weight and non-optimal center of gravity

Pairing, Ferromagnetism, and Condensation of a normal spin-1 Bose gas

We theoretically study the stability of a normal, spin disordered, homogenous spin-1 Bose gas against ferromagnetism, pairing, and condensation through a Random Phase Approximation which includes exchange (RPA-X). Repulsive spin-independent interactions stabilize the normal state against both ferromagnetism and pairing, and for typical interaction strengths leads to a direct transition from an unordered normal state to a fully ordered single particle condensate. Atoms with much larger spin-dependent interaction may experience a transition to a ferromagnetic normal state or a paired superfluid, but, within the RPA-X, there is no instability towards a normal state with spontaneous nematic order. We analyze the role of the quadratic Zeeman effect and finite system size.Comment: 4 pages, 3 figures, 1 table. Supplementary materials attache