Spontaneous Breaking of Translational Invariance in One-Dimensional Stationary States on a Ring

We consider a model in which positive and negative particles diffuse in an asymmetric, CP-invariant way on a ring. The positive particles hop clockwise, the negative counterclockwise and oppositely-charged adjacent particles may swap positions. Monte-Carlo simulations and analytic calculations suggest that the model has three phases; a "pure" phase in which one has three pinned blocks of only positive, negative particles and vacancies, and in which translational invariance is spontaneously broken, a "mixed" phase with a non-vanishing current in which the three blocks are positive, negative and neutral, and a disordered phase without blocks.Comment: 7 pages, LaTeX, needs epsf.st

Yang-Lee Theory for a Nonequilibrium Phase Transition

To analyze phase transitions in a nonequilibrium system we study its grand canonical partition function as a function of complex fugacity. Real and positive roots of the partition function mark phase transitions. This behavior, first found by Yang and Lee under general conditions for equilibrium systems, can also be applied to nonequilibrium phase transitions. We consider a one-dimensional diffusion model with periodic boundary conditions. Depending on the diffusion rates, we find real and positive roots and can distinguish two regions of analyticity, which can identified with two different phases. In a region of the parameter space both of these phases coexist. The condensation point can be computed with high accuracy.Comment: 4 pages, accepted for publication in Phys.Rev.Let

Stratigraphy of offshore sediment of Lake Agassiz, North Dakota

Lake Agassiz occupied the Red River Valley between about 13,800 and 9,000 years ago. The Late Wisconsinan ice sheet that covered the Red River Valley retreated far enough to expose the drainage divide in northern South Dakota and south-central Minnesota sometime after 14,000 B.P. and meltwater ponded behind this divide in Richland County. Before 13,800 the ice readvanced over this area and then retreated again. As the ice margin retreated northward, deposition of the Argusville and Wylie Formations took place. Sometime before 12,800 the ice advanced again into the Red River Valley as far as Traill County; the terminus of this advance is marked by the clay rich pebble-loam of the Huot Formation, and the Falconer Formation was deposited behind the Huot. Deposition of the Argusville Formation continued in the southern part of the basin. Deposition of the Brenna Formation began when the ice margin began retreating out of the Red River Valley. About 11,000 B.P. an eastern outlet into the Lake Superior basin was opened, and Lake Agassiz dropped from the Campbell level to below the Ojata level. During the period between 11,000 B.P. and 9,900 B.P. the lake level fluctuated several times, but most of the time the lake floor was subject to erosion. A stream network similar to that of the present day developed, depositing the Poplar River Formadon. About 9,900 B.P. the eastern outlets were plugged by ice and Lake Agassiz rose back to the Campbell level. The lake stood at this level for about 900 years; during this time the Sherack Formation was deposited. The engineering properties of the Sherack Formation include low to moderate water content (17% to 56%), wide range of liquid limit (27% to 92%), and wide range of consistency index (22% to 86%). The northern part of the Brenna Formation has high water content (62% to 88%), a high liquid limit (63% to 104%), and very low penetration resistance (4 to 7 blows per foot). The southern part of the Brenna Formation and the Wylie and Argusville Formations have similar engineering properties. The range in water content (38% to 69%), liquid limit (39% to 93%), and penetration resistance (4 to 16 blows per foot) for these units are similar. The Poplar River Formation is under confined piezometric conditions, and pilings or footings in it are subject to failure. The Falconer and Huot Formations have engineering properties similar to the Sherack, Wylie, and Argusville Formations. The glacial sediments underlying the Lake Agassiz sediment provide a suitable foundation for nearly all types of construction

Dynamical coupled-channels: the key to understanding resonances

Recent developments on a dynamical coupled-channels model of hadronic and electromagnetic production of nucleon resonances are summarized.Comment: Invited Plenary talk at the 20th European Conference on Few-Body Problems in Physics (EFB20), September 10-14 2007, Pisa, Italy. To appear in the proceedings in Few-Body System

Extraction of the D13(1520) photon-decay couplings from pion- and eta-photoproduction data

We compare results for the D13(1520) photon-decay amplitudes determined in analyses of eta- and pion-photoproduction data. The ratio of helicity amplitudes (A_3/2 / A_1/2), determined from eta-photoproduction data, is quite different from that determined in previous analyses of pion-photoproduction data. We consider how strongly the existing pion-photoproduction data constrain both this ratio and the individual photon-decay amplitudes.Comment: 7 pages, 2 figure

Thermodynamics of Delta resonances

The thermodynamic potential of a system of pions and nucleons is computed including the piN interactions in the P33 channel. A consistent treatment of the width of the resonance in this channel, the Delta(1232) resonance, is explored in detail. In the low-density limit we recover the leading term of the virial expansion for the thermodynamic potential. An instructive diagrammatic interpretation of the contributions to the total baryon number is presented. Furthermore, we examine within a fireball model the consequences for the pion spectra in heavy-ion collisions at intermediate energies, including the effect of collective flow. A consistent treatment of the Delta width leads to a substantial enhancement of the pion yield at low momenta.Comment: 12 pages, 3 Postscript figures, LaTeX, elsart, epsfig, minor changes, references added, to be published in Physics Letters

Matter-wave interferometer for large molecules

We demonstrate a near-field Talbot-Lau interferometer for C-70 fullerene molecules. Such interferometers are particularly suitable for larger masses. Using three free-standing gold gratings of one micrometer period and a transversally incoherent but velocity-selected molecular beam, we achieve an interference fringe visibility of 40 % with high count rate. Both the high visibility and its velocity dependence are in good agreement with a quantum simulation that takes into account the van der Waals interaction of the molecules with the gratings and are in striking contrast to a classical moire model.Comment: revtex4, 4 pages, 3 figure