Zero-temperature magnetism in the periodic Anderson model in the limit of large dimensions

We study the magnetism in the periodic Anderson model in the limit of large dimensions by mapping the lattice problem into an equivalent local impurity self-consistent model. Through a recently introduced algorithm based on the exact diagonalization of an effective cluster hamiltonian, we obtain solutions with and without magnetic order in the half-filled case. We find the exact AFM-PM phase boundary which is shown to be of $2^{nd}$ order and obeys $\frac{V^2}{U} \approx const.$ We calculate the local staggered moments and the density of states to gain insights on the behavior of the AFM state as it evolves from itinerant to a local-moment magnetic regimeComment: 9 pages + 9 figures, to appear in Phys. Rev. B, 1 Sept. 1995 issu

Elementary Transition Systems and Refinement

The model of Elementary Transition Systems has been introduced by the authors as an abstraction of Elementary Net Systems - with a formal embedding in terms of a categorical coreflection, keeping behavioural information like causality, concurrency and conflict, but forgetting the concrete programming of a particular behaviour over an event set using conditions. In this paper we give one example of the advantages of ETS over ENS, - the definition of local state refinement. We show that the well known problems in understanding within nets the simple notion of syntactic substitution of conditions by (sub) nets behaviourally, - these problems seem to disappear when moving to the more abstract level of ETS. Formally, we show that the ETS-version of condition-substitution does satisfy nice and natural properties, e.g., projection and compositionality results w.r.t. a standard notion of transition system morphisms

Elementary Transition Systems and Refinement

The model of Elementary Transition Systems has been introduced by the authors as an abstraction of Elementary Net Systems - with a formal embedding in terms of a categorical coreflection, keeping behavioural information like causality, concurrency and conflict, but forgetting the concrete programming of a particular behaviour over an event set using conditions. In this paper we give one example of the advantages of ETS over ENS, - the definition of local state refinement. We show that the well known problems in understanding within nets the simple notion of syntactic substitution of conditions by (sub) nets behaviourally, - these problems seem to disappear when moving to the more abstract level of ETS. Formally, we show that the ETS-version of condition-substitution does satisfy nice and natural properties, e.g., projection and compositionality results w.r.t. a standard notion of transition system morphisms

Transition Systems, Event Structures and Unfoldings

Elementary transition systems were introduced by the authors in DAIMI PB-310. They were proved to be, in a strong categorical sense, the transition system version of elementray net systems. The question arises whether the notion of a region and the axioms (mostly based on regions) imposed on ordinary transition systems to obtain elementray net systems. Stated differently, one colud ask whether elementray transition systems could also play a role in characterizing other models of concurrency. We show here that by smoothly stengthening the axioms of elementary transition systems one obtains a subclass called occurrence transitions systems which turn out to be categorically equivalent to the well-known model of concurrency called prime event structures. Next we show that occurrence transition systems are to elementry transition systems what occurrence nets are to elementary nets systems. We define an ''unfold'' operation on elementry transition systems which yields occurrence transistion systems. We then prove that this operation uniquely extends to a functor which is the right adjoint to the inclusion functor from (the full subcategory of) occurrence transition systems to (the category of) elementary transition systems. Thus the results of this paper also show that the semantic theory of elementray net systems has a nice counterpart in the more abstract world of transition systems

Elementary Transition Systems and Refinement

The model of Elementary Transition Systems has been introduced by the authors as an abstraction of Elementary Net Systems - with a formal embedding in terms of a categorical coreflection, keeping behavioural information like causality, concurrency and conflict, but forgetting the concrete programming of a particular behaviour over an event set using conditions. In this paper we give one example of the advantages of ETS over ENS, - the definition of local state refinement. We show that the well known problems in understanding within nets the simple notion of syntactic substitution of conditions by (sub) nets behaviourally, - these problems seem to disappear when moving to the more abstract level of ETS. Formally, we show that the ETS-version of condition-substitution does satisfy nice and natural properties, e.g., projection and compositionality results w.r.t. a standard notion of transition system morphisms

Earthquake Risk Management: A Scenario Generator

This paper presents a software package EDGE, an Earthquake Damage Generator/Estimator for Toscana, Italy. EDGE creates samples of multidimentional distributions of damage using models of geophysical processes, seismic-geophysical data and a catalog of vulnerability of buildings in the region. The main algorithmic elements: seismic maps, geophysical formulas, and stochastic modeling, are described in detail. The work contributes to a joint research program of Dynamic Systems, and Risk, Modeling and Society projects on data-based methodological support for decision making in the insurance industry against risks of natural catastrophes. The designed catalogs of expected damages can be used for actuarial calculations and optimization of the regional insurance portfolio

Quantum and thermal fluctuations in the SU(N) Heisenberg spin-glass model near the quantum critical point

We solve for the SU(N) Heisenberg spin-glass in the limit of large N focusing on small S and T. We study the effect of quantum and thermal fluctuations in the frequency dependent response function and observed interesting transfers of spectral weight. We compute the T-dependence of the order parameter and the specific heat and find an unusual T^2 behavior for the latter at low temperatures in the spin-glass phase. We find a remarkable qualitative agreement with various experiments on the quantum frustrated magnet SrCr_{9p}Ga_{12-9p}O_{19}.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let

Serializing the Parallelism in Parallel Communicating Pushdown Automata Systems

We consider parallel communicating pushdown automata systems (PCPA) and define a property called known communication for it. We use this property to prove that the power of a variant of PCPA, called returning centralized parallel communicating pushdown automata (RCPCPA), is equivalent to that of multi-head pushdown automata. The above result presents a new sub-class of returning parallel communicating pushdown automata systems (RPCPA) called simple-RPCPA and we show that it can be written as a finite intersection of multi-head pushdown automata systems