Overlapping risk adjusted sets of priors and the existence of efficient allocations and equilibria with short-selling

The theory of existence of equilibrium with short-selling is reconsidered under risk and ambiguity modelled by risk averse variational preferences. A sufficient condition for existence of efficient allocations is that the relative interiors of the risk adjusted sets of expectations overlap. This condition is necessary if agents are not risk neutral at extreme levels of wealths either positive or negative. It is equivalent to the condition that there does not exist mutually compatible trades, with non negative expected value with respect to any risk adjusted prior, strictly positive for some agent and some prior. It is shown that the more uncertainty averse and the more risk averse the agents, the more likely are efficient allocations and equilibria to exist.Uncertainty;risk;common prior;equilibria with shortselling;Variational preferences

No-arbitrage, overlapping sets of priors and the existence of efficient allocations and equilibria in the presence of risk and ambiguity

The theory of existence of equilibrium with short-selling is reconsidered under risk and ambiguity modelled by risk averse variational preferences. A sufficient condition for existence of efficient allocations is that the relative interiors of the risk adjusted sets of expectations overlap. This condition is necessary if agents are not risk neutral at extreme levels of wealths either positive or negative. It is equivalent to the condition that there does not exist mutually compatible trades, with non negative expected value with respect to any risk adjusted prior, strictly positive for some agent and some prior. It is shown that the more uncertainty averse and the more risk averse, the more likely are efficient allocations and equilibria to exist.Uncertainty, risk, common prior, equilibria with short-selling, variational preferences.

Overlapping sets of priors and the existence of efficient allocations and equilibria for risk measures

The overlapping expectations and the collective absence of arbitrage conditions introduced in the economic literature to insure existence of Pareto optima and equilibria when short-selling is allowed and investors hold a single belief about future returns, is reconsidered. Investors use measures of risk. The overlapping sets of priors and the Pareto equilibrium conditions introduced by Heath and Ku for coherent risk measures are reinterpreted as a weak no-arbitrage and a weak collective absence of arbitrage conditions and shown to imply existence of Pareto optima and Arrow Debreu equilibria.Overlapping sets of priors, collective absence of arbitrage, equilibria with short-selling, risk sharing, measures of risk.

Overlapping sets of priors and the existence of efficient allocations and equilibria for risk measures

The overlapping expectations and the collective absence of arbitrage conditions introduced in the economic literature to insure existence of Pareto optima and equilibria with short-selling when investors have a single belief about future returns, is reconsidered. Investors use measures of risk. The overlapping sets of priors and the Pareto equilibrium conditions introduced by Heath and Ku for coherent risk measures are respectively reinterpreted as a weak no-arbitrage and a weak collective absence of arbitrage conditions and shown to imply existence of Pareto optima and Arrow-Debreu equilibria.Overlapping sets of priors;collective absence of arbitrage;equilibria with short-selling;measures of risk

Gli alunni stranieri e l’apprendimento delle matematica: alcune riflessioni sul caso italiano

The growing presence of foreign students in the Italian school continually interrogate teachers, policy makers and all those who are daily faced with issues related to this more and more structural reality. This work presents an analysis of the educational achievements in Mathematics of foreign students who have just completed the first cycle of education (5th grade) in Italy. To this end, we use INVALSI data that have the advantage to measure learning outcomesthrough standardized tests. Studying the frequency of responding correctly to any individual item and controlling for students’ background, we find substantially different and more encouraging reading of the learning gaps between Italian and foreign students.La crescente presenza di allievi stranieri nella scuola italiana interroga continuamente gli insegnanti, i decisori politici e tutti coloro che si trovano quotidianamente a fronteggiare le problematiche legate a questa realtà sempre più strutturale. Il presente contributo propone un’analisi sugli esiti in Matematicaalle Rilevazioni INVALSI 2014 degli studenti con cittadinanza non italiana che hanno appena terminato il primo ciclo di istruzione (classe V della scuola primaria). Considerando la probabilità di rispondere correttamente ai singoli item e tenendo sotto controllo alcune condizioni di contesto, si può avere una lettura diversa e più incoraggiante dei divari nell’apprendimento tra alunni italiani e stranieri

Optical memory bandwidth and multiplexing capacity in the erbium telecommunication window

We study the bandwidth and multiplexing capacity of an erbium-doped optical memory for quantum storage purposes. We concentrate on the protocol ROSE (Revival of a Silenced Echo) because it has the largest potential multiplexing capacity. Our analysis is applicable to other protocols that involve strong optical excitation. We show that the memory performance is limited by instantaneous spectral diffusion and we describe how this effect can be minimised to achieve optimal performance

Influence of Road Speed Restrictions on the Incidence and Severity of Head Injuries

A comparative survey has been made of patients with head injuries admitted to hospital in 1973 and 1974, before and after the introduction of fuel-saving measures, which included road speed restrictions. The severity and incidence of injury are shown to have decreased dramatically. It is concluded from this that the main cause of the improvement has been reduce:l road traffic speeds. A plea is made that they be permanently maintained

Student Understandings of Information Systems Design, Learning and Teaching: A Phenomenography Approach

Phenomenographic studies have shown clear links between the approach students take to learning and the achievement of deep versus surface learning outcomes in higher education. The context in which learning takes place is a key factor in these studies. The purpose of this research is to discover the conceptions of learning, teaching and information systems design held by a diverse group of 60 second-year university students and to determine whether there are differences between field-dependent and field-independent students. Our context-dependent findings on student conceptions of teaching and learning are descriptive in nature. These findings were integrated into an outcome space of student conceptions of information systems design, which is interpreted with respect to existing theory on differences between field-dependent and field-independent students and the cognitive demands of learning information systems design. The results have implications for teaching practice and further research on the effects of qualitative variations in student conceptions on the achievement of deep versus surface levels of learning about information systems design