Mean Field Solution of the Random Ising Model on the Dual Lattice

We perform a duality transformation that allows one to express the partition function of the d-dimensional Ising model with random nearest neighbor coupling in terms of new spin variables defined on the square plaquettes of the lattice. The dual model is solved in the mean field approximation.Comment: TeX file 10 pages, 2 figures available under request to Paladin at vxscaq.aquila.infn.i

L'opera di Vezio Crisafulli tra diritto e politica

Pur con tutti i limiti delle operazioni di revisione costituzionale, delle quali Crisafulli si mostrava consapevole, il suo sguardo era dunque rivolto in avanti e non verso il passato. Se gli fossero stati concessi altri anni di vita, egli avrebbe certamente preso parte alle tante controversie, politiche, giurisprudenziali e dottrinali, che hanno accompagnato e seguito il crollo del tradizionale quadro politico italiano. Rimane per me il solo dubbio sulle sue reazioni al confuso dibattito che sta accompagnando l'attuale tentativo di una grande riforma. Sarebbero prevalsi il suo spirito polemico oppure il senso civico di cui parlava Nocilla? Che cosa avrebbe pensato Crisafulli del cosiddetto federalismo all'italiana, del semipresidenzialismo oscillante tra la Francia e l'Austria, della Corte costituzionale alterata e gravata da innumerevoli compiti? Questo -purtroppo- lo possiamo soltanto immaginare

Beyond the Mean Field Approximation for Spin Glasses

We study the d-dimensional random Ising model using a Bethe-Peierls approximation in the framework of the replica method. We take into account the correct interaction only inside replicated clusters of spins. Our ansatz is that the interaction of the borders of the clusters with the external world can be described via an effective interaction among replicas. The Bethe-Peierls model is mapped into a single Ising model with a random gaussian field, whose strength (related to the effective coupling between two replicas) is determined via a self-consistency equation. This allows us to obtain analytic estimates of the internal energy and of the critical temperature in d dimensions.Comment: plane TeX file,19 pages. 3 figures may be requested to Paladin at axscaq.aquila.infn.i

Constrained annealing for spin glasses

The quenched free energy of spin glasses is estimated by means of annealed averages where the frustration is constrained to its average value. We discuss the case of d-dimensional Ising models with random nearest neighbour coupling, and we introduce a new method to obtain constrained annealed averages without recurring to Lagrange multipliers. It requires to perform quenched averages either on small volumes in an analytic way, or on finite size strips via products of random transfer matrices. We thus give a sequence of converging lower bounds for the quenched free energy of 2d spin glasses.Comment: plane TeX file,24 pages. 6 figures may be requested to Paladin at vxscaq.aquila.infn.i

Dejavniki neverbalne komunikacije v povezavi s prepričljivostjo posameznika

Poleg verbalnih sporočil so v komunikaciji zelo pomembna neverbalna sporočila,saj jim praviloma zaupamo bolj kot verbalni komponenti komunikacije. Ena od funkcij neverbalne komunikacije je prepričevanje. Dosedanje raziskave so pokazale, da očesni stik, slog oblačenja, določene vokalične značilnosti ter nekatere vrste dotika vplivajo na prepričljivost posameznika. Raziskava, ki smo jo izvedli, je pokazala, da anketiranci menijo,da je za nekoga, ki želi biti prepričljiv, pomembno, kako določeno informacijo posreduje. Na oblikovanje mnenj o vplivu znakov neverbalne komunikacije na prepričljivost vplivajo različni dejavniki. Rezultati naše raziskave so pokazali nekatere zanimive razlike v primerjavi z dosedanjimi raziskavami

Laž in laganje

Laž in laganje sta tako del vsakdanjega življenja kot tudi del managementa. Najbolj strnjeno bi lahko rekli, da je namen laži z namernim zavajanjem škodovati nekomu. Kanalov za zaznavanje laži in laganja je veliko: višina, glasnost, hitrost, jasnost in vsebina govora, očesni gibi, geste z rokami ter telesni in obrazni gibi. Sklepanje o neiskrenosti govorca na podlagi enega samega znaka je lahko zavajajoče. Nujno je upoštevati več znakov hkrati ter iskati nekonsistentnost med njimi. Pogledi na vlogo laži in laganja v managementu so različni. Medtem ko sta za nekatere laž in laganje del igre, sta za druge nedopustna in nezaželena

Stochastic Resonance in Deterministic Chaotic Systems

We propose a mechanism which produces periodic variations of the degree of predictability in dynamical systems. It is shown that even in the absence of noise when the control parameter changes periodically in time, below and above the threshold for the onset of chaos, stochastic resonance effects appears. As a result one has an alternation of chaotic and regular, i.e. predictable, evolutions in an almost periodic way, so that the Lyapunov exponent is positive but some time correlations do not decay.Comment: 9 Pages + 3 Figures, RevTeX 3.0, sub. J. Phys.

Lack of self-average in weakly disordered one dimensional systems

We introduce a one dimensional disordered Ising model which at zero temperature is characterized by a non-trivial, non-self-averaging, overlap probability distribution when the impurity concentration vanishes in the thermodynamic limit. The form of the distribution can be calculated analytically for any realization of disorder. For non-zero impurity concentration the distribution becomes a self-averaging delta function centered on a value which can be estimated by the product of appropriate transfer matrices.Comment: 17 pages + 5 figures, TeX dialect: Plain TeX + IOP macros (included

The (im)possibility of reducing the meteotsunami amplitude by constructing protective breakwaters

Plitkovodni gravitacijski val uzrokovan gibanjem atmosferskog poremećaja povećava svoju amplitudu kroz energetski transfer omogućen Proudmanovom rezonancijom. Nailaskom na lučki bazen oblika lijevka dešava se dodatna amplificija valnog signala. Ukoliko valna grupa koja nailazi sadrži i frekvencije bliske lučkim vlastitim frekvencijama moguća je i pojava rezonancije s daljnjim povećenjem valnih amplituda. Cjelokupna pojava naziva se meteocunami, a primjer te pojave desio se i 21.6.1978. u Veloj Luci, pri čemu su registrirane valne visine od 6 m. U radu je provedena numerička analiza dinamike morskih razi u krajnjoj točki Vele Luke uslijed valne pobude s maksimalnim visinama od 0,19 m ispred ulaza u zaljev Vela Luka. Kao odgovor na valnu pobudu u krajnjoj točki luke dobivene su valne visine od 5,5 m. Analiziran je utjecaj hipotetskih vertikalnih nepropusnih lukobrana, na valne visine u samoj Veloj luci. Korištene su dvije varijante pozicije ispred ulaza u Velu Luku. Modelski rezultati ukazuju na relativno malo smanjenje valnih visina.Shallow water gravity wave caused by motion of atmospheric disturbances increases its amplitude through energy transfer enabled by the Proudman resonance. The waveform signals get further amplified reaching the funnel shaped port basin. If the incoming wave group contains frequencies close to the port\u27s eigen frequencies the resonance with a further increase of wave amplitude is likely to occur. The whole phenomenon is called meteotsunami, and an example of this phenomenon occurred on 21 June 1978 in Vela Luka, where the wave height was registered to be 6 m. The paper deals with carrying out the numerical analysis of the sea level dynamics in the final point brought about due to wave excitation with a maximum height of 0,19 m in front of the entrance to the Vela Luka Bay. In response to the wave excitation in the port\u27s final point, the obtained wave height was 5,5 m. Furthermore, the analysis involving the influence of hypothetical vertical impermeable breakwaters, set on two variant positions outside the entrance to Vela Luka was carried out. The model results indicate that there is a relatively small decrease in wave height

Predictability in Systems with Many Characteristic Times: The Case of Turbulence

In chaotic dynamical systems, an infinitesimal perturbation is exponentially amplified at a time-rate given by the inverse of the maximum Lyapunov exponent $\lambda$. In fully developed turbulence, $\lambda$ grows as a power of the Reynolds number. This result could seem in contrast with phenomenological arguments suggesting that, as a consequence of `physical' perturbations, the predictability time is roughly given by the characteristic life-time of the large scale structures, and hence independent of the Reynolds number. We show that such a situation is present in generic systems with many degrees of freedom, since the growth of a non-infinitesimal perturbation is determined by cumulative effects of many different characteristic times and is unrelated to the maximum Lyapunov exponent. Our results are illustrated in a chain of coupled maps and in a shell model for the energy cascade in turbulence.Comment: 24 pages, 10 Postscript figures (included), RevTeX 3.0, files packed with uufile