A multilayered effective medium model for the roughness effect on the Casimir force

A multilayered effective medium model is proposed to calculate the contribution of surface roughness to the Casimir force. In this model the rough layer has its optical properties derived from an effective medium approximation, with the rough layer considered as the mixing of voids and solid material. The rough layer can be divided into sublayers consisting of different volume fractions of voids and solid material as a function of the roughness surface profile. The Casimir force is then calculated using the generalizations of the Lifshitz theory for multilayered planar systems. Predictions of the Casimir force based on the proposed model are compared with those of well known methods of calculation, usually restricted to be used with large scale roughness. It is concluded that the effect of short scale roughness as predicted by this model is considerably larger than what could be expected from the extrapolation of the results obtained by the other methods

A credit contagion model for the dynamics of the rating transitions in a SME bank loan portfolio

In this work we analyze the effects of credit contagion on the credit quality of a portfolio of bank loans issued to SMEs. To this aim we start from the discrete time model proposed in Barro and Basso (2005), that considers the counterparty risk generated by the business relations in a network of firms, and we modify it by introducing different rating classes in order to manage the case of firms with different credit qualities. The transitions from a rating class to another occurs when a proxy for the asset value of the firm crosses some rating specific thresholds. We assume that the initial rating transition matrix of the system is known, and compute the thresholds using the probability distribution of the steady state of the model. A wide Monte Carlo simulation analysis is carried out in order to study the dynamic behaviour of the model, and in particular to analyze how the default contagion present in the model affects the output rating transition matrix of the portfolio.

Urn-based models for dependent credit risks and their calibration through EM algorithm

In this contribution we analyze two models for the joint probability of defaults of dependent credit risks that are based on a generalisation of Polya urn scheme. In particular we focus our attention on the problems related to the maximum likelihood estimation of the parameters involved, and to this purpose we introduce an approach based on the use of the Expectation-Maximization algorithm. We show how to implement it in this context, and then we analyze the results obtained, comparing them with results obtained by other approaches.

Particle Swarm Optimization with non-smooth penalty reformulation for a complex portfolio selection problem

In the classical model for portfolio selection the risk is measured by the variance of returns. It is well known that, if returns are not elliptically distributed, this may cause inaccurate investment decisions. To address this issue, several alternative measures of risk have been proposed. In this contribution we focus on a class of measures that uses information contained both in lower and in upper tail of the distribution of the returns. We consider a nonlinear mixed-integer portfolio selection model which takes into account several constraints used in fund management practice. The latter problem is NP-hard in general, and exact algorithms for its minimization, which are both effective and efficient, are still sought at present. Thus, to approximately solve this model we experience the heuristics Particle Swarm Optimization (PSO). Since PSO was originally conceived for unconstrained global optimization problems, we apply it to a novel reformulation of our mixed-integer model, where a standard exact penalty function is introduced.Portfolio selection, coherent risk measure, fund management constraints, NP-hard mathematical programming problem, PSO, exact penalty method, SP100 index's assets.

Can Four-fermion Contact Interactions at One-loop Explain the New Atomic Parity Violation Results?

We investigate the possibility that four-fermion contact interactions giverise to the observed deviation from the Standard Model prediction for the weakcharge of Cesium, through one-loop contributions. We show that the presence ofloops involving the third generation quarks can explain such deviation

Optimization of administrative processes in beer export : a case study

Amidst the expanding global trade landscape, the effective management of global supply chains (GSCs) has become a crucial concern for multinational corporations, significantly impacting their performance. In the context of the beer industry, maritime transportation, particularly through container shipments, plays a pivotal role, influencing and being influenced by various interconnected chains. In 2022, Heineken's French subsidiary faced a €10,000 loss due to inconsistencies in customs clearance documentation, a crucial aspect of export operations. In response, this study presents an approach aimed at optimizing customs document transmission, grounded in a thorough process analysis. This approach involves two optimization strategies: the automation of repetitive tasks through VBA programming and SAP macros, and the reduction of errors through systematic checklists

Milanosifastoria: una Rete e un Progetto per la valorizzazione culturale e formativa della storia ‘locale’ di Milano

L’esposizione del progetto Milanosifastoria prende avvio dalle sue motivazioniche si basano sull’esigenza di rilanciare la culturastorica mettendo in rete una pluralità di soggettisensibili agli intrecci fra ricerca, documentazione,divulgazione e didattica storica e interessatia valorizzare il patrimonio storico-culturalemilanese attraverso il dialogo fra persone di diversigeneri, generazioni, specializzazioni e culture.Tale rete, formalizzata con un protocollo d’intesacol Comune di Milano, condivide la volontà diconnettere in chiave interdisciplinare i diversiambiti degli studi storici, da quello delle ricerchea quello della didattica e della diffusione, diavvalersi del dialogo interculturale, di promuovereiniziative partecipate e interattive. A partire daquella del 2014 ogni edizione di Milanosifastoria approfondirà una tematica monografica e sisvolgerà nell’arco di un anno accademico/scolastico per favorire la partecipazione attivaanche di università e scuole. La prima edizioneha come tema la storia della istruzione/formazione/educazione nell’area milanese e inaltre aree comparabili nell’intento di dare rilievoa tali aspetti colmandone il vuoto di conoscenza