Further comments on the background field method and gauge invariant effective actions

The aim of this paper is to give a firm and clear proof of the existence in the background field framework of a gauge invariant effective action for any gauge theory ({\it background gauge equivalence}). Here by effective action we mean a functional whose Legendre transform restricted to the physical shell generates the matrix elements of the connected $S$-matrix. We resume and clarify a former argument due to Abbott, Grisaru and Schaefer based on the gauge-artifact nature of the background fields and on the identification of the gauge invariant effective action with the generator of the proper, background field, vertices.Comment: 21 pages, Latex 2

A Functional and Lagrangian Formulation of Two-Dimensional Topological Gravity

We reconsider two-dimensional topological gravity in a functional and lagrangian framework. We derive its Slavnov-Taylor identities and discuss its (in)dependence on the background gauge. Correlators of reparamerization invariant observables are shown to be globally defined forms on moduli space. The potential obstruction to their gauge-independence is the non-triviality of the line bundle on moduli space ${\cal L}_x$, whose first Chern-class is associated to the topological invariants of Mumford, Morita and Miller. Based on talks given at the Fubini Fest, Torino, 24-26 February 1994, and at the Workshop on String Theory, Trieste, 20-22 April 1994.Comment: 11 pages, harvmac, CERN-TH-7302/94, GEF-Th-6/199

Training Designers of the Future: Reflections on a Didactic Case ‘Made in Italy’

Focusing on a specific case, the postgraduate course Product Service System Design taught in English to Italian and international students of the Design Facult y at Milan Pol ytechnic, the author reflects on the present and future of designers as ‘reflexive professionals’ (to quote Donald A. Schön1) called upon to act in uncertain and vaguely defined contexts, tackle problems in highly original ways and come up with wide -ranging, experimental and innovative solutions resorting to complex and hybrid techniques and tools either purposely designed or taken from other fields

A graph-dynamical interpretation of Kiselman's semigroups

A Sequential Dynamical System (SDS) is a quadruple (\Gamma, S_i,f_i,w) consisting of a (directed) graph \Gamma=(V,E), each of whose vertices i\in V is endowed with a finite set state S_i and an update function f_i: \prod_{j, i \to j} S_j \to S_i --- we call this structure an {\em update system} --- and a word w in the free monoid over V, specifying the order in which update functions are to be performed. Each word induces an evolution of the system and in this paper we are interested in the dynamics monoid, whose elements are all possible evolutions. When \Gamma is a directed acyclic graph, the dynamics monoid of every update system supported on \Gamma naturally arises as a quotient of the Hecke-Kiselman monoid associated with \Gamma. In the special case where \Gamma = \Gamma_n is the complete oriented acyclic graph on n vertices, we exhibit an update system whose dynamics monoid coincides with Kiselman's semigroup K_n, thus showing that the defining Hecke-Kiselman relations are optimal in this situation. We then speculate on how these results may extend to the general acyclic case.Comment: 14 pages. This is a substantial revision of the previous version. Proofs and exposition have been simplified. The title has been changed to better reflect the content of the pape

Wind loads analysis at the anchorages of the Talavera de la Reina cable stayed bridge

This paper describes wind tunnel tests performed on wind tunnel models of the Talavera de la Reina cable stayed bridge. The work describes the aeroelastic model construction and it is focused on the evaluation and analysis of the mean and peak wind loads at the tower foundation and the cable anchorages since these data can be very useful by the bridge manufacturer as a support for the bridge design. The work is part of a complete wind tunnel study carried out to analyze the aeroelastic stability of the bridge

Repeated Contracting with Multiple Non-Myopic Agents: Policy Regret and Limited Liability

We study a repeated contracting setting in which a Principal adaptively chooses amongst $k$ Agents at each of $T$ rounds. The Agents are non-myopic, and so a mechanism for the Principal induces a $T$-round extensive form game amongst the Agents. We give several results aimed at understanding an under-explored aspect of contract theory -- the game induced when choosing an Agent to contract with. First, we show that this game admits a pure-strategy \emph{non-responsive} equilibrium amongst the Agents -- informally an equilibrium in which the Agent's actions depend on the history of realized states of nature, but not on the history of each other's actions, and so avoids the complexities of collusion and threats. Next, we show that if the Principal selects Agents using a \emph{monotone} bandit algorithm, then for any concave contract, in any such equilibrium, the Principal obtains no regret to contracting with the best Agent in hindsight -- not just given their realized actions, but also to the counterfactual world in which they had offered a guaranteed $T$-round contract to the best Agent in hindsight, which would have induced a different sequence of actions. Finally, we show that if the Principal selects Agents using a monotone bandit algorithm which guarantees no swap-regret, then the Principal can additionally offer only limited liability contracts (in which the Agent never needs to pay the Principal) while getting no-regret to the counterfactual world in which she offered a linear contract to the best Agent in hindsight -- despite the fact that linear contracts are not limited liability. We instantiate this theorem by demonstrating the existence of a monotone no swap-regret bandit algorithm, which to our knowledge has not previously appeared in the literature

dynamic simulation and critical assessment of a composite bridge in high speed railway

Abstract Evaluation of critical responses of a bridge including resonances in high-speed (HS) railway is a dominant issue in order to confirm the structural safety of bridge and the stability of ballast on bridge deck. In numerical way for critical assessment, it is important to make a sophisticated numerical model and considering the variation of actual properties of structural members. This study proposed a train-track-bridge interaction model focusing on Sesia viaduct, and calibrated the model properties as matching these modal characteristics and dynamic responses to measured ones. By the numerical and experimental comparison, calibrated model could reproduce accelerations up to 30 Hz both of on the time and frequency domains accurately. Especially, good agreements on sleeper accelerations can indicate the high reproducibility of interaction force, which is one of key factors of train-track-bridge interaction simulation. Numerical computation by calibrated model clarified that the deck acceleration up to 30Hz increases by seventh and eighth resonances between passing vehicle length and structural modes, not only global third bending or third torsional but also high order local deck modes. In addition, high performance computing technique based on super computer in RTRI was adopted for parametric analysis in order to investigate the requirements to realize highly accurate estimation for the maximum deck acceleration by the numerical way. As the results of parametric study focusing on design assumption, calculation modal order and train/bridge interaction, it was clarified that the design model causes overestimation by twice maximum acceleration on the deck, and the amplification of excitation forces caused by passage on deflected rails, which is considered in high-order modes and train/bridge interaction, is a key factor to achieve accurate deck acceleration evaluation

Railway Bridge Runability Safety Analysis in a Vessel Collision Event

Abstract: Bridges connecting islands close to the coast and crossing the sea have been attracting the attention of several researchers working in the field of train–bridge interactions. A runability analysis of a bridge during the event of a ship impact with a pier is one of the most interesting and challenging scenarios to simulate. The objective of the present paper is to study the impact on the running safety of a train crossing a sea bridge as a function of different operational factors, such as the train travelling speed, the type of impacting ship, and the impact force magnitude. Considering train–bridge interactions, a focus is also placed on wheel–rail geometrical contact profiles, considering new and worn wheel–rail profiles. This work is developed considering a representative continuous deck bridge with pier foundations located on the sea bed composed of six spans of 80 m. Time-domain simulations of trains running on the bridge during ship impact events were carried out to quantify the effect of different operating parameters on the train running safety. For this purpose, derailment and unloading coefficients, according to railway standards, were calculated from wheel–rail vertical and lateral contact forces. Maps of the safety coefficients were finally built to assess the combined effect of the impact force magnitude and train speed. The present investigation also showed that new wheel–rail contact geometrical profiles represent the most critical case compared to moderately worn wheel–rail profiles

A New Approach: Determining cyt b G143A Allele Frequency in Zymoseptoria tritici by Digital Droplet PCR

Z. tritici first appeared in Italy later than in northern-central European countries. QoIs fungicides currently play a role in STB control, used in combination with Demethylation Inhibitors (DMIs) or Succinate dehydrogenase Inhibitors (SDHIs). In this study, we set up a fast, sensitive, and accurate ddPCR protocol in order to investigate the presence and frequency of G143A substitution, causing a reduction in strobilurins’ efficacy in Z. tritici. The best PCR conditions for the clear separation of positive and negative droplets were identified. The lowest wild-type and resistant alleles frequencies were accurately determined on samples consisting of mixed DNAs from monoconidial cultures of Z. tritici and were expressed as fractional abundance. The protocol was tested by determining the copy number and frequency of alleles on gDNA purified in three Italian Z. tritici field populations representative of different fungicide management strategies. For the first time, the determination of allele concentration and the frequency of a mutation involved in Z. tritici fungicide resistance was carried out by employing digital PCR. This new approach provides a diagnostic tool that is rapid and able to detect very low G143A substitution percentages, which is very useful for fungicide resistance detection at early stages, thus, informing field management strategies for contrasting STB disease