Lightweight Security for Network Coding

Under the emerging network coding paradigm, intermediate nodes in the network are allowed not only to store and forward packets but also to process and mix different data flows. We propose a low-complexity cryptographic scheme that exploits the inherent security provided by random linear network coding and offers the advantage of reduced overhead in comparison to traditional end-to-end encryption of the entire data. Confidentiality is achieved by protecting (or "locking") the source coefficients required to decode the encoded data, without preventing intermediate nodes from running their standard network coding operations. Our scheme can be easily combined with existing techniques that counter active attacks.Comment: Proc. of the IEEE International Conference on Communications (ICC 2008), Beijing, China, May 200

The Equivalence Principle Revisited

A precise formulation of the strong Equivalence Principle is essential to the understanding of the relationship between gravitation and quantum mechanics. The relevant aspects are reviewed in a context including General Relativity, but allowing for the presence of torsion. For the sake of brevity, a concise statement is proposed for the Principle: "An ideal observer immersed in a gravitational field can choose a reference frame in which gravitation goes unnoticed". This statement is given a clear mathematical meaning through an accurate discussion of its terms. It holds for ideal observers (time-like smooth non-intersecting curves), but not for real, spatially extended observers. Analogous results hold for gauge fields. The difference between gravitation and the other fundamental interactions comes from their distinct roles in the equation of force.Comment: RevTeX, 18 pages, no figures, to appear in Foundations of Physic

Hospital production in a national health service: the physician's dilemma

There is a paucity of literature concerning the relation between the resource utilization decisions of the salaried hospital based physician and patient outcomes in a national health service. The purpose of our study is to model and test hospital production where the major decision makers are physicians. We view the output of the hospital as a distribution function over final health states of the patient. Our model contains a utility function for physicians whose arguments include the expected final health status of the patient and a pressure function which reflects the resource allocation and hospital financing policy of the Portuguese Health Ministry. Two sets of first order conditions derived from the theoretical model are estimated within a simultaneous equations framework using data consisting of inpatient discharges for the most frequent non-obstetric DRG during the 1992-1999 time period. We find evidence that budget setting methods and the possession of a third party payer outside of the NHS are important predictors for use of the resource in question. Moreover, we find that use of the resource is important in predicting the final health status of the patient.

Preventive health care and payment systems to providers

Prevention has been a main issue of recent policy orientations in health care. This renews the interest on how different organizational designs and the definition of payment schemes to providers may affect the incentives to provide preventive health care. We present, both the normative and the positive analyses of the change from independent providers to integrated services. We show the evaluation of that change to depend on the particular way payment to providers is done. We focus on the externality resulting from referral decisions from primary to acute care providers. This makes our analysis complementary to most works in the literature allowing to address in a more direct way the issue of preventive health care.Preventive health care, payment systems to providers

Unlearned Lessons from Risk, Debt Service, Bank Credit, and Asymmetric Information

This paper presents a model of the economy that explains the economic bubbles, based on bank credit, debt service and risk. In the first period of the model, banks offer too much credit seeking to maximise their expected profits. The excessive debt created in the boom period generates, in the second-period, the expansion of the debt bubble, which induces failures in the financial market and the downturn of the overall economy. Business cycles are inherent in the free market systems. They may be caused by endogenous factors of financial markets and, given the absence of adequate, effective regulation, they may be unavoidable. Credit crunch in the financial market is therefore highly probable. In order to reduce substantially the risk of such occurrences, economic and financial policies are proposed. Key words: Asymmetric information, bank credit, risk, debt service and business cycle

Comments on "There is no axiomatic system for the quantum theory"

In a recent paper, Nagata [1] claims to derive inconsistencies from quantum mechanics. In this paper, we show that the inconsistencies do not come from quantum mechanics, but from extra assumptions about the reality of observables

Decision Making for Inconsistent Expert Judgments Using Negative Probabilities

In this paper we provide a simple random-variable example of inconsistent information, and analyze it using three different approaches: Bayesian, quantum-like, and negative probabilities. We then show that, at least for this particular example, both the Bayesian and the quantum-like approaches have less normative power than the negative probabilities one.Comment: 14 pages, revised version to appear in the Proceedings of the QI2013 (Quantum Interactions) conferenc

Moral hazard and the demand for health services: A matching estimator approach

We estimate the impact of extra health insurance coverage beyond a National Health System on the demand for several health services. Traditionally, the literature has tried to deal with the endogeneity of the private (extra) insurance decision by finding instrumental variables. Since a priori instrumental variables are hard to find we take a different approach. We focus on the most common health insurance plan in Portugal, ADSE, which is given to all civil servants and their dependents. We argue that this insurance is exogenous, i.e., not correlated with the beneficiaries’ health status. This identifying assumption allows us to estimate the impact of having ADSE coverage on the demand for three different health services using a matching estimator technique. The health services used are number of visits, number of blood and urine tests, and the probability of visiting a dentist. Results show large positive effects of ADSE coverage for number of visits and tests among the young (18–30 years old) but only the latter is statistically significantly different from zero. The effects represent 21.8% and 30% of the average number of visits and tests for the young. On the contrary, we find no evidence of moral hazard on the probability of visiting a dentist.Publicad