Decoherence in a dynamical quantum phase transition

Motivated by the similarity between adiabatic quantum algorithms and quantum phase transitions, we study the impact of decoherence on the sweep through a second-order quantum phase transition for the prototypical example of the Ising chain in a transverse field and compare it to the adiabatic version of Grovers search algorithm, which displays a first order quantum phase transition. For site-independent and site-dependent coupling strengths as well as different operator couplings, the results show that (in contrast to first-order transitions) the impact of decoherence caused by a weak coupling to a rather general environment increases with system size (i.e., number of spins/qubits). This might limit the scalability of the corresponding adiabatic quantum algorithm.Comment: 14 pages, 9 figure

Empirical logic of finite automata: microstatements versus macrostatements

We compare the two approaches to the empirical logic of automata. The first, called partition logic (logic of microstatements), refers to experiments on individual automata. The second one, the logic of simulation (logic of macrostatements), deals with ensembles of automata.Comment: late

How do the grains slide in fine-grained zirconia polycrystals at high temperature?

Degradation of mechanical properties of zirconia polycrystals is hardly discussed in terms of solution-precipitation grain-boundary sliding due to experimental controversies over imaging of intergranular amorphous phases at high and room temperatures. Here, the authors applied the techniques of mechanical spectroscopy and transmission electron microscopy (TEM) to shed light on the amorphization of grain interfaces at high temperature where the interface-reaction determines the behaviour of fine-grained zirconia polycrystals. They present mechanical spectroscopy results, which yield evidences of an intergranular amorphous phase in silica doped and high-purity zirconia at high temperature. Quenching of zirconia polycrystals reveals an intergranular amorphous phase on TEM images at room temperature.Comment: 12 pages, 3 figure

The East German Cement Cartel : An Inquiry into Comparable Markets, Industry Structure, and Antitrust Policy

Maintaining sufficient levels of competition ranks among the core interests of any national – and increasingly international – antitrust policy; however, the formal proof that a cartel really functioned economically and did not only exist in a legal sense is hard to deliver: market power is not identical to the existence of a legal cartel unless the monopolistic frontier is reached; the legal proof of a cartel does not imply that the market was harmed. From an economic point of view, focusing on legal proof of a cartel is fruitless unless collusion resulted in excess profits or excess revenues. This economic evidence, however, rests empirically on the proper definition of comparable markets, and a sound statistical methodology. When in spring 2003, the German Antitrust Agency (GAA) fined the German cement industry – € 661 million for having established quotas in each of the four market regions through the end of 2001, the legal issue seemed beyond doubt as, beside formal inquiries, two of the industry members had acted as key witnesses. However, the economic implications drawn by the GAA remain doubtful. In this paper, we use the quota agreement in the East German market, the region for which these allegations are undisputed by all major suppliers, as a reference case. We challenge the GAA’s computation of excess income of 10 €/ton on two grounds: (i), the comparative market period chosen, 2002, does not meet the requirements of a reference market, especially regarding a certain level of stability and converging prices; (ii) three parallel developments could have triggered the price decline: the openly announced end of the quota cartel, which generated general price-setting insecurity (ii-a), the price war triggered by one of the oligopolists, who desperately tried to improve poor utilization of capacity and squeeze out competitors (ii-b), and the general decline in construction activity (ii-c). Within the framework of an econometric model based on data of one German cement producer, we find that sufficient levels of competition prevailed throughout the cartel period. Furthermore, the demand structure did not change from 2001 to 2002 so as to suggest a fundamental change in competition. Finally, no excess income or profit can be computed. In fact, we show that the general demand regime estimated for the period 1995 to 2001, which is the period of alleged market power, equally well describes the market condition of 2002. Price war and a collapsing construction market lead suppliers to maintain levels of production and capacity utilization, thus sacrificing profits at the expense of the market shares of small and medium-sized suppliers independently from the cartel issue. This empirical finding of an agreed but ineffective cartel is supported by theoretical evidence on the conditions under which cartels can work effectively – which did not exist in the East: strong import competition, a high level of transparency limiting the effects of „cheap talk“ and spatial pricing that generates local market power in the absence of cartels. Furthermore, general supply-side conditions in the cement industry suggest that a considerable level of imperfect competition is structurally unavoidable; antitrust possibilities that in the short run enforce additional competition based on the wrong assessment of effective collusion may lead to exits and less competition in the long run. We conclude that the methodology described may be useful for antitrust policy as it offers a credible analytical tool to compute excess income and profit. --antitrust,cement,competition,collusion,Germany,econometrics,excess income,excess profit,quota agreement

A Photometric System for Detection of Water and Methane Ices on Kuiper Belt Objects

We present a new near-infrared photometric system for detection of water ice and methane ice in the solar system. The system consists of two medium-band filters in the K-band region of the near-infrared, which are sensitive to water ice and methane ice, plus continuum observations in the J-band and Y-band. The primary purpose of this system is to distinguish between three basic types of Kuiper Belt Objects (KBOs) --- those rich in water ice, those rich in methane ice, and those with little absorbance. In this work, we present proof-of-concept observations of 51 KBOs using our filter system, 21 of which have never been observed in the near-IR spectroscopically. We show that our custom photometric system is consistent with previous spectroscopic observations while reducing telescope observing time by a factor of 3. We use our filters to identify Haumea collisional family members, which are thought to be collisional remnants of a much larger body and are characterized by large fractions of water ice on their surfaces. We add 2009 YE7 to the Haumea collisional family based on our water ice band observations(J-H2O = -1.03 +/- 0.27) which indicate a high amount of water ice absorption, our calculated proper orbital elements, and the neutral optical colors we measured, V-R = 0.38 +/- 0.04, which are all consistent with the rest of the Haumea family. We identify several objects dynamically similar to Haumea as being distinct from the Haumea family as they do not have water ice on their surfaces. In addition, we find that only the largest KBOs have methane ice, and we find that Haumea itself has significantly less water ice absorption than the smaller Haumea family members. We find no evidence for other families in the Kuiper Belt.Comment: 38 pages, 7 figure

The Nature of [Ar III] Bright Knots in the Crab Nebula

The kinematic and morphological properties of a string of [Ar III] bright knots in the Crab Nebula are examined using 1994 - 1999 HST WFPC-2 images of the remnant. We find that five southern [Ar III] bright knots exhibit ordinary radial motions away from the nebula's center of expansion with magnitudes consistent with their projected radial displacements. These results do not support the suggestion by MacAlpine et al.(1994) that these knots might be moving rapidly away from the Crab pulsar due to a collimated wind. The HST images also do not show that the [Ar III] knots have unusual morphologies relative to other features in the remnant. Our proper motion results, when combined with radial velocity estimates, suggest these knots have relatively low space velocities implying relatively interior remnant locations thus placing them closer to the ionizing radiation from the Crab's synchrotron nebula. This might lead to higher knot gas temperatures thereby explaining the knots' unusual line emission strengths as MacAlpine et al.(1994) suspected.Comment: 11 pages including three figures. Submitted to the Astronomical Journa

Generalized 2d dilaton gravity with matter fields

We extend the classical integrability of the CGHS model of 2d dilaton gravity [1] to a larger class of models, allowing the gravitational part of the action to depend more generally on the dilaton field and, simultaneously, adding fermion- and U(1)-gauge-fields to the scalar matter. On the other hand we provide the complete solution of the most general dilaton-dependent 2d gravity action coupled to chiral fermions. The latter analysis is generalized to a chiral fermion multiplet with a non-abelian gauge symmetry as well as to the (anti-)self-dual sector df = *df (df = -*df) of a scalar field f.Comment: 37 pages, Latex; typos and Eqs. (44,45) corrected; paragraph on p. 26, referring to a work of S. Solodukhin, reformulated; references adde

Determinants for the Timing of Escapement From the Sockeye Salmon Fishery of the Copper River, Alaska: A Simulation Model

A model to estimate determinants for migratory timing of catch and escapement in a terminal salmon fishery is presented. A method was developed to estimate average seasonal migration rates of salmon through a harvest area from catch and escapement data. The time series for the total population of Copper River sockeye salmon (Oncorhynchus nerka) was reconstructed in the reference frame of the commercial harvest area from catch and escapement data. The catchability coefficients (q), derived from the reconstructed populations were found to vary within season and between seasons. The relation between q and effort was attributed to a highly competitive fishery. The difference found between the descriptive statistics for the time densities of catch and catch per unit of effort (CPUE) are attributed to varying q. In a highly competitive terminal fishery the time density of catch was found to be a better representation of the time density of total abundance than that of CPUE. The comparison of the time series of daily proportions of catch and CPUE was found to be a valuable diagnostic tool for determining whether q was variable over a season. It was inferred from the reconstructed time series of total abundance that escapement from the commercial harvest area was underestimated by the sonar counter. The under estimation of escapement from the commercial harvest area may be attributed to two sources; (1) the delta stocks are higher than point estimates found by stock separation studies; (2) the enumeration of escapement to the upper Copper River spawning areas are being underestimated by the sonar counter. The simulation model was a useful tool for investigating the behavior of migratory time densities and for evaluating the success of alternative management strategies in terms of distributing an escapement goal proportionately over time

Discovery of Temperate Latitude Clouds on Titan

Until now, all the clouds imaged in Titan's troposphere have been found at far southern latitudes (60°-90° south). The occurrence and location of these clouds is thought to be the result of convection driven by the maximum annual solar heating of Titan's surface, which occurs at summer solstice (2002 October) in this south polar region. We report the first observations of a new recurring type of tropospheric cloud feature, confined narrowly to ~40° south latitude, which cannot be explained by this simple insolation hypothesis. We propose two classes of formation scenario, one linked to surface geography and the other to seasonally evolving circulation, which will be easily distinguished with continued observations over the next few years

Classical and Quantum Gravity in 1+1 Dimensions, Part III: Solutions of Arbitrary Topology

All global solutions of arbitrary topology of the most general 1+1 dimensional dilaton gravity models are obtained. We show that for a generic model there are globally smooth solutions on any non-compact 2-surface. The solution space is parametrized explicitly and the geometrical significance of continuous and discrete labels is elucidated. As a corollary we gain insight into the (in general non-trivial) topology of the reduced phase space. The classification covers basically all 2D metrics of Lorentzian signature with a (local) Killing symmetry.Comment: 39 pages, 22 figures, uses AMSTeX, extended version of former chapter 7 (Gravitational Kinks) now available as gr-qc/9707053, problem with figure 6 fixe